<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2023 Workiva-->
<!--r:8e7dc951-4656-4e03-a0e8-4e50df8fe096,g:f5c18480-9888-4845-bcad-0e48f49dbc08-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.ducommun.com/role/ConsolidatedStatementsofChangesinShareholdersEquity" xlink:type="simple" xlink:href="dco-20221231.xsd#ConsolidatedStatementsofChangesinShareholdersEquity"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/ConsolidatedStatementsofChangesinShareholdersEquity" xlink:type="extended" id="ib13e8296501241e98fe58f702eb262eb_ConsolidatedStatementsofChangesinShareholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_a7cfcb00-9830-4de8-af8e-220373dd64a4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a7cfcb00-9830-4de8-af8e-220373dd64a4" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_c3212494-dad3-420a-803d-782ed2ff7133" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_c3212494-dad3-420a-803d-782ed2ff7133" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_ab69d00e-ccd6-4bad-a3e7-f7e77d8a82ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockholdersEquity_ab69d00e-ccd6-4bad-a3e7-f7e77d8a82ef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_02dfff31-4c45-4632-a6ab-60f702218a7c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_NetIncomeLoss_02dfff31-4c45-4632-a6ab-60f702218a7c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_65993688-2c1c-4e73-8e6a-bb90b2fc85ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_65993688-2c1c-4e73-8e6a-bb90b2fc85ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_25c4b001-d3b7-4f36-a14c-45ae379d652c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_25c4b001-d3b7-4f36-a14c-45ae379d652c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_ee635719-5598-4c92-8733-38a770d7b7c4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_ee635719-5598-4c92-8733-38a770d7b7c4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_9bda45e0-ed5c-41ed-9f9c-826653f973de" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_9bda45e0-ed5c-41ed-9f9c-826653f973de" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_599fa551-4f05-4070-8f6c-1a542ff2096e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_599fa551-4f05-4070-8f6c-1a542ff2096e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_bf787a22-d3ae-4eea-8552-14ca1687b8e5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_bf787a22-d3ae-4eea-8552-14ca1687b8e5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_dfbe8ae8-858f-4da4-96c7-a9354971776f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_dfbe8ae8-858f-4da4-96c7-a9354971776f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_17dc8c66-0666-45c9-b989-94e6339cae1f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_17dc8c66-0666-45c9-b989-94e6339cae1f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_ef95b0a7-0354-4b1b-8f7b-e3c6ab15bb7e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_ef95b0a7-0354-4b1b-8f7b-e3c6ab15bb7e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f378a316-1960-4e00-aa2d-1291e4a661b9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6d58d819-aa3a-4ffb-82d1-f1de7cc19487" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f378a316-1960-4e00-aa2d-1291e4a661b9" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_3cb50473-c461-4924-8161-f719cc3957d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_dd102ed7-3ac6-4260-8a7f-aec1c246bafc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_535da3e3-faf8-4ef6-a3ac-267fa77436df" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_a7cfcb00-9830-4de8-af8e-220373dd64a4" xlink:to="loc_us-gaap_StatementTable_535da3e3-faf8-4ef6-a3ac-267fa77436df" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_f4221086-05ba-4be5-b64c-e1b7bd8d1aa4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_535da3e3-faf8-4ef6-a3ac-267fa77436df" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_f4221086-05ba-4be5-b64c-e1b7bd8d1aa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_f4221086-05ba-4be5-b64c-e1b7bd8d1aa4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_f4221086-05ba-4be5-b64c-e1b7bd8d1aa4" xlink:to="loc_us-gaap_EquityComponentDomain_f4221086-05ba-4be5-b64c-e1b7bd8d1aa4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_60c11529-c652-4f0e-8ae1-581fa8b31624" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_f4221086-05ba-4be5-b64c-e1b7bd8d1aa4" xlink:to="loc_us-gaap_EquityComponentDomain_60c11529-c652-4f0e-8ae1-581fa8b31624" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_64724973-e767-42dd-be47-c30aad50787e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60c11529-c652-4f0e-8ae1-581fa8b31624" xlink:to="loc_us-gaap_CommonStockMember_64724973-e767-42dd-be47-c30aad50787e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_32111991-b12d-4345-a0b6-5aacf4dd67ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60c11529-c652-4f0e-8ae1-581fa8b31624" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_32111991-b12d-4345-a0b6-5aacf4dd67ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_4b8303ca-200f-49cc-a04f-56eb1a66dcf9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60c11529-c652-4f0e-8ae1-581fa8b31624" xlink:to="loc_us-gaap_RetainedEarningsMember_4b8303ca-200f-49cc-a04f-56eb1a66dcf9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_0646166d-9bf9-4b6f-b22b-2548e7a4a096" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60c11529-c652-4f0e-8ae1-581fa8b31624" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_0646166d-9bf9-4b6f-b22b-2548e7a4a096" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended" id="ic72f1912a9094ffab554db7f13257037_SummaryofSignificantAccountingPoliciesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:href="dco-20221231.xsd#dco_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_74035108-d7a0-419c-a5c8-5c7cf960fad0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_NumberOfReportableSegments_74035108-d7a0-419c-a5c8-5c7cf960fad0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedPremium_63d6a3cb-99f5-44ed-b9f6-8cfddb5a1920" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentUnamortizedPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedPremium_63d6a3cb-99f5-44ed-b9f6-8cfddb5a1920" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_913f1d3e-f3b3-4430-9b43-7e927ec9806d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_DerivativeNotionalAmount_913f1d3e-f3b3-4430-9b43-7e927ec9806d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_ce8004cc-0858-4955-9029-e1e8b1f19a0f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_ce8004cc-0858-4955-9029-e1e8b1f19a0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_HedgedAssetFairValueHedgeAdjustmentDueToUnderstatement_152a6d7d-df77-452d-9f84-2a6aa17963f1" xlink:href="dco-20221231.xsd#dco_HedgedAssetFairValueHedgeAdjustmentDueToUnderstatement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_dco_HedgedAssetFairValueHedgeAdjustmentDueToUnderstatement_152a6d7d-df77-452d-9f84-2a6aa17963f1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease_1287d37f-294f-47fe-98b9-a49dd010762a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_HedgedAssetFairValueHedgeCumulativeIncreaseDecrease_1287d37f-294f-47fe-98b9-a49dd010762a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_e55c7bcb-b904-4c54-9d17-6f6b8f9d8a5a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_e55c7bcb-b904-4c54-9d17-6f6b8f9d8a5a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_93e73d60-12c5-44c7-a613-1e3e58e701d8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_Goodwill_93e73d60-12c5-44c7-a613-1e3e58e701d8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_e5f53a12-b78b-4fa9-9a7d-f2147e8f5666" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_e5f53a12-b78b-4fa9-9a7d-f2147e8f5666" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_70f6ae23-a5ef-4b07-8ead-a273d92fadf0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_70f6ae23-a5ef-4b07-8ead-a273d92fadf0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e80c3aca-93a6-4289-ab26-04547280e264" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e80c3aca-93a6-4289-ab26-04547280e264" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_308d1df0-4ef6-446a-8739-3f0ec3c059c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_308d1df0-4ef6-446a-8739-3f0ec3c059c6" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProductionCostOfContractsCurrent_1ed6abff-4d8f-4969-8438-10fc6e451f37" xlink:href="dco-20221231.xsd#dco_ProductionCostOfContractsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_dco_ProductionCostOfContractsCurrent_1ed6abff-4d8f-4969-8438-10fc6e451f37" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_a012d0b5-a6e7-4bd4-9171-21d97bb826c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_a012d0b5-a6e7-4bd4-9171-21d97bb826c3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantsReceivable_fc2147f3-de10-4743-8d8d-c308b221df62" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GrantsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_us-gaap_GrantsReceivable_fc2147f3-de10-4743-8d8d-c308b221df62" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProceedsReceivedFromGrants_14f9e968-f3bf-4ed2-8eac-d982699f3a1b" xlink:href="dco-20221231.xsd#dco_ProceedsReceivedFromGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_dco_ProceedsReceivedFromGrants_14f9e968-f3bf-4ed2-8eac-d982699f3a1b" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GovernmentGrantExpense_560dcf30-bfd9-455c-a556-565f0549647b" xlink:href="dco-20221231.xsd#dco_GovernmentGrantExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_dco_GovernmentGrantExpense_560dcf30-bfd9-455c-a556-565f0549647b" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MiscellaneousExpenses_491048f7-db0c-4e4e-9428-32862171744d" xlink:href="dco-20221231.xsd#dco_MiscellaneousExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_dco_MiscellaneousExpenses_491048f7-db0c-4e4e-9428-32862171744d" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:href="dco-20221231.xsd#dco_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_ebaeb096-fa18-460c-bcf4-b43688b7b2f8" xlink:to="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_8f584e91-e09b-49ce-aac8-9aa57f57fa2e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_8f584e91-e09b-49ce-aac8-9aa57f57fa2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_8f584e91-e09b-49ce-aac8-9aa57f57fa2e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_8f584e91-e09b-49ce-aac8-9aa57f57fa2e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_8f584e91-e09b-49ce-aac8-9aa57f57fa2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_721469d3-8a56-468c-a242-a3a2146d5590" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_8f584e91-e09b-49ce-aac8-9aa57f57fa2e" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_721469d3-8a56-468c-a242-a3a2146d5590" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMember_ea83e6c2-acae-4caf-b749-3a2b7fe61a7e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_721469d3-8a56-468c-a242-a3a2146d5590" xlink:to="loc_us-gaap_OtherAssetsMember_ea83e6c2-acae-4caf-b749-3a2b7fe61a7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_2792b20d-e3e7-46fa-a7cb-7fb85e55dfae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_2792b20d-e3e7-46fa-a7cb-7fb85e55dfae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_2792b20d-e3e7-46fa-a7cb-7fb85e55dfae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2792b20d-e3e7-46fa-a7cb-7fb85e55dfae" xlink:to="loc_us-gaap_SegmentDomain_2792b20d-e3e7-46fa-a7cb-7fb85e55dfae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_2a5d941b-f546-4829-a80a-1eb6a07b4294" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2792b20d-e3e7-46fa-a7cb-7fb85e55dfae" xlink:to="loc_us-gaap_SegmentDomain_2a5d941b-f546-4829-a80a-1eb6a07b4294" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_ad788769-4aca-4c45-8ab3-bf8a71c3e404" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2a5d941b-f546-4829-a80a-1eb6a07b4294" xlink:to="loc_dco_ElectronicSystemsSegmentMember_ad788769-4aca-4c45-8ab3-bf8a71c3e404" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_d682761c-2122-44d1-b193-86b9f96aadf0" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_2a5d941b-f546-4829-a80a-1eb6a07b4294" xlink:to="loc_dco_StructuralSystemsSegmentMember_d682761c-2122-44d1-b193-86b9f96aadf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_a7d3b797-acc1-4cd5-a26c-ba93571aa443" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_a7d3b797-acc1-4cd5-a26c-ba93571aa443" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a7d3b797-acc1-4cd5-a26c-ba93571aa443_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_a7d3b797-acc1-4cd5-a26c-ba93571aa443" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a7d3b797-acc1-4cd5-a26c-ba93571aa443_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f21d9238-441d-47aa-b193-1c38df9a309c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_a7d3b797-acc1-4cd5-a26c-ba93571aa443" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f21d9238-441d-47aa-b193-1c38df9a309c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_29ea5817-1317-43ad-851d-d7b33c49b800" xlink:href="dco-20221231.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f21d9238-441d-47aa-b193-1c38df9a309c" xlink:to="loc_dco_MagneticSealCorporationMember_29ea5817-1317-43ad-851d-d7b33c49b800" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_144c4287-d954-4881-a32b-c2814d27aedc" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:to="loc_srt_RangeAxis_144c4287-d954-4881-a32b-c2814d27aedc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_144c4287-d954-4881-a32b-c2814d27aedc_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_144c4287-d954-4881-a32b-c2814d27aedc" xlink:to="loc_srt_RangeMember_144c4287-d954-4881-a32b-c2814d27aedc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b0780fb1-521b-49cc-87c0-80b3d949add6" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_144c4287-d954-4881-a32b-c2814d27aedc" xlink:to="loc_srt_RangeMember_b0780fb1-521b-49cc-87c0-80b3d949add6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_9e10421b-8bfe-47ec-95cf-3d16e17c9f00" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b0780fb1-521b-49cc-87c0-80b3d949add6" xlink:to="loc_srt_MinimumMember_9e10421b-8bfe-47ec-95cf-3d16e17c9f00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_ee7a67d8-125c-41d8-808c-66eb2f499183" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b0780fb1-521b-49cc-87c0-80b3d949add6" xlink:to="loc_srt_MaximumMember_ee7a67d8-125c-41d8-808c-66eb2f499183" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_f9239be7-5b8f-4f94-b9e8-c67070ef9fdf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:to="loc_us-gaap_HedgingDesignationAxis_f9239be7-5b8f-4f94-b9e8-c67070ef9fdf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_f9239be7-5b8f-4f94-b9e8-c67070ef9fdf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_f9239be7-5b8f-4f94-b9e8-c67070ef9fdf" xlink:to="loc_us-gaap_HedgingDesignationDomain_f9239be7-5b8f-4f94-b9e8-c67070ef9fdf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_8525eda0-d926-4e03-9ae0-d4f2af3330ea" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_f9239be7-5b8f-4f94-b9e8-c67070ef9fdf" xlink:to="loc_us-gaap_HedgingDesignationDomain_8525eda0-d926-4e03-9ae0-d4f2af3330ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_a3271c1e-63df-45da-a72f-7f87f71d2724" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_8525eda0-d926-4e03-9ae0-d4f2af3330ea" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_a3271c1e-63df-45da-a72f-7f87f71d2724" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_faf46b3c-6e94-40ef-a08b-5134f0f0caa6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_faf46b3c-6e94-40ef-a08b-5134f0f0caa6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_faf46b3c-6e94-40ef-a08b-5134f0f0caa6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_faf46b3c-6e94-40ef-a08b-5134f0f0caa6" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_faf46b3c-6e94-40ef-a08b-5134f0f0caa6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_8262a580-9cc3-400d-964a-ffcc4a641821" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_faf46b3c-6e94-40ef-a08b-5134f0f0caa6" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_8262a580-9cc3-400d-964a-ffcc4a641821" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_c64e8123-3260-4e23-99f5-6f82a57cc8cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_8262a580-9cc3-400d-964a-ffcc4a641821" xlink:to="loc_us-gaap_CostOfSalesMember_c64e8123-3260-4e23-99f5-6f82a57cc8cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_70069696-c0ef-475b-a699-4743241753a4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_8262a580-9cc3-400d-964a-ffcc4a641821" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_70069696-c0ef-475b-a699-4743241753a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_6ef5313d-9665-4fbb-ba4e-4e14f3ccac1b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_90486dc2-a2f5-4ebd-b71b-88dfe21e9231" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_6ef5313d-9665-4fbb-ba4e-4e14f3ccac1b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_6ef5313d-9665-4fbb-ba4e-4e14f3ccac1b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6ef5313d-9665-4fbb-ba4e-4e14f3ccac1b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_6ef5313d-9665-4fbb-ba4e-4e14f3ccac1b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_0f2e0068-436a-43ef-8f80-e03fc0503da7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6ef5313d-9665-4fbb-ba4e-4e14f3ccac1b" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_0f2e0068-436a-43ef-8f80-e03fc0503da7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_a46df5aa-4ecf-40d7-9a99-d667548bb81f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_0f2e0068-436a-43ef-8f80-e03fc0503da7" xlink:to="loc_us-gaap_InterestRateSwapMember_a46df5aa-4ecf-40d7-9a99-d667548bb81f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails" xlink:type="extended" id="id695d1e2557a44ac8844a4e84be13e0f_SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_4eb3745c-7843-47df-99b5-d0a603677b85" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_4eb3745c-7843-47df-99b5-d0a603677b85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5f6cab62-66e3-4436-963a-e95340f9732a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5f6cab62-66e3-4436-963a-e95340f9732a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_e092be05-1978-49d1-8359-0d4f5a4d0186" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_e092be05-1978-49d1-8359-0d4f5a4d0186" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_ad87e965-4cc3-43b5-91dd-9c5cf458cc9e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_e092be05-1978-49d1-8359-0d4f5a4d0186" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_ad87e965-4cc3-43b5-91dd-9c5cf458cc9e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails_1" xlink:type="simple" xlink:href="dco-20221231.xsd#SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails_1"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails_1" xlink:type="extended" id="i17c4891d757b4a959986a4d2b8a89dbd_SummaryofSignificantAccountingPoliciesRemainingPerformanceObligationDetails_1">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_4eb3745c-7843-47df-99b5-d0a603677b85" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_4eb3745c-7843-47df-99b5-d0a603677b85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5f6cab62-66e3-4436-963a-e95340f9732a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_5f6cab62-66e3-4436-963a-e95340f9732a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_e092be05-1978-49d1-8359-0d4f5a4d0186" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_158fc6d6-e5bb-4df7-957a-2d77709f7c29" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_e092be05-1978-49d1-8359-0d4f5a4d0186" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails" xlink:type="extended" id="id79ddbd516834153b0e547753df83598_SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_7f7cfe9d-ee5b-4ec5-ab20-9bea51de3d03" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_IncreaseDecreaseinRevenuefromContractwithCustomers_651fcfb2-a730-4a5d-b3a7-0578136e62b8" xlink:href="dco-20221231.xsd#dco_IncreaseDecreaseinRevenuefromContractwithCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_7f7cfe9d-ee5b-4ec5-ab20-9bea51de3d03" xlink:to="loc_dco_IncreaseDecreaseinRevenuefromContractwithCustomers_651fcfb2-a730-4a5d-b3a7-0578136e62b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b7b27f1c-ccfd-4117-80ca-548e024da950" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_7f7cfe9d-ee5b-4ec5-ab20-9bea51de3d03" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b7b27f1c-ccfd-4117-80ca-548e024da950" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PercentageOfRevenuesFromContractWithCustomers_fcbe30e7-063e-4d95-9871-1747809e5123" xlink:href="dco-20221231.xsd#dco_PercentageOfRevenuesFromContractWithCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_7f7cfe9d-ee5b-4ec5-ab20-9bea51de3d03" xlink:to="loc_dco_PercentageOfRevenuesFromContractWithCustomers_fcbe30e7-063e-4d95-9871-1747809e5123" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_f2c1ef75-f4b1-412e-887e-0cb0d45c2fbe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_7f7cfe9d-ee5b-4ec5-ab20-9bea51de3d03" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_f2c1ef75-f4b1-412e-887e-0cb0d45c2fbe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_a7868784-b24a-461d-b819-9fd3a1c038bf" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f2c1ef75-f4b1-412e-887e-0cb0d45c2fbe" xlink:to="loc_srt_ProductOrServiceAxis_a7868784-b24a-461d-b819-9fd3a1c038bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a7868784-b24a-461d-b819-9fd3a1c038bf_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_a7868784-b24a-461d-b819-9fd3a1c038bf" xlink:to="loc_srt_ProductsAndServicesDomain_a7868784-b24a-461d-b819-9fd3a1c038bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_5bbf7429-63d7-4c30-a882-fdc56521137a" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_a7868784-b24a-461d-b819-9fd3a1c038bf" xlink:to="loc_srt_ProductsAndServicesDomain_5bbf7429-63d7-4c30-a882-fdc56521137a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MilitaryandSpaceMember_2b21df52-0797-4958-be17-2a3b1143575f" xlink:href="dco-20221231.xsd#dco_MilitaryandSpaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5bbf7429-63d7-4c30-a882-fdc56521137a" xlink:to="loc_dco_MilitaryandSpaceMember_2b21df52-0797-4958-be17-2a3b1143575f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_CommercialAerospaceMember_dd16278a-2fd8-43d9-8d29-b7e9dd459541" xlink:href="dco-20221231.xsd#dco_CommercialAerospaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5bbf7429-63d7-4c30-a882-fdc56521137a" xlink:to="loc_dco_CommercialAerospaceMember_dd16278a-2fd8-43d9-8d29-b7e9dd459541" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_IndustrialMember_92145c4e-bce7-400f-90ce-e21767ce3b4b" xlink:href="dco-20221231.xsd#dco_IndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_5bbf7429-63d7-4c30-a882-fdc56521137a" xlink:to="loc_dco_IndustrialMember_92145c4e-bce7-400f-90ce-e21767ce3b4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_3f4c3e39-526e-4114-9386-62cc099b43a7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_f2c1ef75-f4b1-412e-887e-0cb0d45c2fbe" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_3f4c3e39-526e-4114-9386-62cc099b43a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_3f4c3e39-526e-4114-9386-62cc099b43a7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3f4c3e39-526e-4114-9386-62cc099b43a7" xlink:to="loc_us-gaap_SegmentDomain_3f4c3e39-526e-4114-9386-62cc099b43a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_67198cee-eaa4-4835-aa59-ff02d959a3eb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_3f4c3e39-526e-4114-9386-62cc099b43a7" xlink:to="loc_us-gaap_SegmentDomain_67198cee-eaa4-4835-aa59-ff02d959a3eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_aff1b62e-086f-4d8a-bc2a-ab36853dc51e" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_67198cee-eaa4-4835-aa59-ff02d959a3eb" xlink:to="loc_dco_ElectronicSystemsSegmentMember_aff1b62e-086f-4d8a-bc2a-ab36853dc51e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_4378b837-3d49-4208-a63e-17b7ec88acd3" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_67198cee-eaa4-4835-aa59-ff02d959a3eb" xlink:to="loc_dco_StructuralSystemsSegmentMember_4378b837-3d49-4208-a63e-17b7ec88acd3" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails" xlink:type="extended" id="i80b328d611dd41b6848cf54bda4318c6_SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_329950a6-5912-4863-9c7f-249067ff6d6b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_cd1928c8-fa60-4ce3-adf9-f4f6e09110dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_329950a6-5912-4863-9c7f-249067ff6d6b" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_cd1928c8-fa60-4ce3-adf9-f4f6e09110dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_10573898-a5cc-4c52-805e-a25414c2682f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_329950a6-5912-4863-9c7f-249067ff6d6b" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_10573898-a5cc-4c52-805e-a25414c2682f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_eed740e6-7ec2-4237-8daa-871b2c9d1a29" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_10573898-a5cc-4c52-805e-a25414c2682f" xlink:to="loc_us-gaap_AwardTypeAxis_eed740e6-7ec2-4237-8daa-871b2c9d1a29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_eed740e6-7ec2-4237-8daa-871b2c9d1a29_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_eed740e6-7ec2-4237-8daa-871b2c9d1a29" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_eed740e6-7ec2-4237-8daa-871b2c9d1a29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_86c0367c-2d5f-4f93-a194-d5c463518c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_eed740e6-7ec2-4237-8daa-871b2c9d1a29" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_86c0367c-2d5f-4f93-a194-d5c463518c0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StockOptionsAndRestrictedStockUnitsMember_cbc34044-08d8-4da5-bf97-5b7bbad87654" xlink:href="dco-20221231.xsd#dco_StockOptionsAndRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_86c0367c-2d5f-4f93-a194-d5c463518c0c" xlink:to="loc_dco_StockOptionsAndRestrictedStockUnitsMember_cbc34044-08d8-4da5-bf97-5b7bbad87654" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessCombinationsNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#BusinessCombinationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessCombinationsNarrativeDetails" xlink:type="extended" id="ia2936a20d34f4e61a2e14e8f116deb20_BusinessCombinationsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_0fe6f5c8-e838-426d-8a17-f3825682c680" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_0fe6f5c8-e838-426d-8a17-f3825682c680" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_8f83915a-dce7-432a-a637-2ba1400123d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_8f83915a-dce7-432a-a637-2ba1400123d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_027923cb-fc29-4adf-be65-96abc8fa6b1e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_027923cb-fc29-4adf-be65-96abc8fa6b1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_c33781be-bdb7-4050-8880-482f21127188" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAcquiredFromAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_c33781be-bdb7-4050-8880-482f21127188" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_c0bc8a1f-096b-4961-b93b-0e563a3c72b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_c0bc8a1f-096b-4961-b93b-0e563a3c72b1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_6c4c8183-4995-45ba-ac13-6baad98a9f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_6c4c8183-4995-45ba-ac13-6baad98a9f8c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_2f5f2887-400a-4c4e-84da-d41fb36ecd78" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_Goodwill_2f5f2887-400a-4c4e-84da-d41fb36ecd78" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_f1e0f10e-1d82-487a-8363-ff73cfc6acbf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_f1e0f10e-1d82-487a-8363-ff73cfc6acbf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_d8665123-4992-4f39-b6d1-8dae191c6f17" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c822308a-ac25-495b-ae23-8947204c0484" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_d8665123-4992-4f39-b6d1-8dae191c6f17" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_a31b5cf8-b52c-44b9-8482-bae89a94366b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_d8665123-4992-4f39-b6d1-8dae191c6f17" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_a31b5cf8-b52c-44b9-8482-bae89a94366b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a31b5cf8-b52c-44b9-8482-bae89a94366b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_a31b5cf8-b52c-44b9-8482-bae89a94366b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_a31b5cf8-b52c-44b9-8482-bae89a94366b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c24f6be8-8cc0-47bb-af26-3e25eb922605" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_a31b5cf8-b52c-44b9-8482-bae89a94366b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c24f6be8-8cc0-47bb-af26-3e25eb922605" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_f8bab8ef-db05-4caa-87d2-3fa7d9dc8cf1" xlink:href="dco-20221231.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c24f6be8-8cc0-47bb-af26-3e25eb922605" xlink:to="loc_dco_MagneticSealCorporationMember_f8bab8ef-db05-4caa-87d2-3fa7d9dc8cf1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails" xlink:type="extended" id="iff20de2b5ff94453b7093a309383058f_BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_1ba188bd-cffe-4830-944c-9679a742f920" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_1ba188bd-cffe-4830-944c-9679a742f920" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_c706b98b-41ec-4a36-8d4f-cff8c3d3981a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_c706b98b-41ec-4a36-8d4f-cff8c3d3981a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_eccab52a-326d-4bd2-9aeb-5d7c1c65d251" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_eccab52a-326d-4bd2-9aeb-5d7c1c65d251" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_1a9d6d6f-df5e-4fb1-b17a-d706a265c610" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_1a9d6d6f-df5e-4fb1-b17a-d706a265c610" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_fde2ac7e-fc18-4ce5-becd-2cf234234d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_fde2ac7e-fc18-4ce5-becd-2cf234234d0e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_23e5463e-c7b7-48d5-909b-d6e2e215f1f8" xlink:href="dco-20221231.xsd#dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_23e5463e-c7b7-48d5-909b-d6e2e215f1f8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_8c213d46-11c5-4423-bc7a-1f5d82b563a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_8c213d46-11c5-4423-bc7a-1f5d82b563a5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_38f95b35-e5dc-413c-8755-cf92619dca38" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_Goodwill_38f95b35-e5dc-413c-8755-cf92619dca38" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedAssets_c9a96afa-2062-4486-bf83-10cc16f5d07f" xlink:href="dco-20221231.xsd#dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedAssets_c9a96afa-2062-4486-bf83-10cc16f5d07f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_75600f4d-aacf-4350-9c0e-f9fff7aee758" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_75600f4d-aacf-4350-9c0e-f9fff7aee758" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_8ec4adf6-dbc2-4aaa-9db4-7d7d01b8c792" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_8ec4adf6-dbc2-4aaa-9db4-7d7d01b8c792" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_be14c392-e8f2-4aa2-8997-90c3af1837e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_be14c392-e8f2-4aa2-8997-90c3af1837e8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_21ec8fe6-b302-4308-a290-f9463f26057f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_21ec8fe6-b302-4308-a290-f9463f26057f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_3e11409a-05d0-48a5-a17f-6eae3fbcfada" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_b4eb0d54-1f18-4d26-998c-b283b8ac9b3d" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_3e11409a-05d0-48a5-a17f-6eae3fbcfada" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_3cc24b9c-43e4-4dd8-a659-9bf5fb80dd2a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_3e11409a-05d0-48a5-a17f-6eae3fbcfada" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_3cc24b9c-43e4-4dd8-a659-9bf5fb80dd2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3cc24b9c-43e4-4dd8-a659-9bf5fb80dd2a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_3cc24b9c-43e4-4dd8-a659-9bf5fb80dd2a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3cc24b9c-43e4-4dd8-a659-9bf5fb80dd2a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c444bc78-3089-48b9-993d-1b7a9ebea57b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_3cc24b9c-43e4-4dd8-a659-9bf5fb80dd2a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c444bc78-3089-48b9-993d-1b7a9ebea57b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_354bb2a5-2a55-4947-b85e-e835fe4739e6" xlink:href="dco-20221231.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_c444bc78-3089-48b9-993d-1b7a9ebea57b" xlink:to="loc_dco_MagneticSealCorporationMember_354bb2a5-2a55-4947-b85e-e835fe4739e6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails" xlink:type="extended" id="ie7d536053c0a47ef81a45ece8f35aa61_BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_17d4a6d5-0a2e-42b3-a1e4-245d3f68b89d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_41ad559d-c66f-4ea1-9217-b2014a12b17c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17d4a6d5-0a2e-42b3-a1e4-245d3f68b89d" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_41ad559d-c66f-4ea1-9217-b2014a12b17c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_63530df8-549e-4fcd-abe7-e663e2c583e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17d4a6d5-0a2e-42b3-a1e4-245d3f68b89d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_63530df8-549e-4fcd-abe7-e663e2c583e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_aa861186-2bea-49e1-a17b-ebc682a4990a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17d4a6d5-0a2e-42b3-a1e4-245d3f68b89d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_aa861186-2bea-49e1-a17b-ebc682a4990a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_e7b29543-964b-47d0-894a-7bfc70b9247f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17d4a6d5-0a2e-42b3-a1e4-245d3f68b89d" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_e7b29543-964b-47d0-894a-7bfc70b9247f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0fd86fdb-d8ca-48c4-9e3a-f5d66de9d03c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17d4a6d5-0a2e-42b3-a1e4-245d3f68b89d" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0fd86fdb-d8ca-48c4-9e3a-f5d66de9d03c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_52034976-2fa0-40c0-a171-30c00f0c00b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0fd86fdb-d8ca-48c4-9e3a-f5d66de9d03c" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_52034976-2fa0-40c0-a171-30c00f0c00b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_52034976-2fa0-40c0-a171-30c00f0c00b1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_52034976-2fa0-40c0-a171-30c00f0c00b1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_52034976-2fa0-40c0-a171-30c00f0c00b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2b9d5d48-e7c1-48f8-be15-5639a16ca28a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_52034976-2fa0-40c0-a171-30c00f0c00b1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2b9d5d48-e7c1-48f8-be15-5639a16ca28a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_fe996582-49e4-40c4-a9e0-5101b2deeddc" xlink:href="dco-20221231.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2b9d5d48-e7c1-48f8-be15-5639a16ca28a" xlink:to="loc_dco_MagneticSealCorporationMember_fe996582-49e4-40c4-a9e0-5101b2deeddc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a92374a2-2943-4b2b-92f9-2d855768f11f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0fd86fdb-d8ca-48c4-9e3a-f5d66de9d03c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a92374a2-2943-4b2b-92f9-2d855768f11f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a92374a2-2943-4b2b-92f9-2d855768f11f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a92374a2-2943-4b2b-92f9-2d855768f11f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a92374a2-2943-4b2b-92f9-2d855768f11f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6491b3fd-5509-464d-b45f-27b2d7579fe5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a92374a2-2943-4b2b-92f9-2d855768f11f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6491b3fd-5509-464d-b45f-27b2d7579fe5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_91937729-cf2f-430c-b574-d5a368ddbb7b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6491b3fd-5509-464d-b45f-27b2d7579fe5" xlink:to="loc_us-gaap_CustomerRelationshipsMember_91937729-cf2f-430c-b574-d5a368ddbb7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OrderOrProductionBacklogMember_32dd8a8a-b1cd-4909-98c2-1c71ea367853" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OrderOrProductionBacklogMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6491b3fd-5509-464d-b45f-27b2d7579fe5" xlink:to="loc_us-gaap_OrderOrProductionBacklogMember_32dd8a8a-b1cd-4909-98c2-1c71ea367853" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_9bfc92e6-fe9e-40af-b33a-4b7e67364d32" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0fd86fdb-d8ca-48c4-9e3a-f5d66de9d03c" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_9bfc92e6-fe9e-40af-b33a-4b7e67364d32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_9bfc92e6-fe9e-40af-b33a-4b7e67364d32_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_9bfc92e6-fe9e-40af-b33a-4b7e67364d32" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_9bfc92e6-fe9e-40af-b33a-4b7e67364d32_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_c2f524ac-2fb8-47f5-9ba0-8d7ee481b9bd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_9bfc92e6-fe9e-40af-b33a-4b7e67364d32" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_c2f524ac-2fb8-47f5-9ba0-8d7ee481b9bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_23b03a98-d41b-4e8d-aedd-ac9f9da8def3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_c2f524ac-2fb8-47f5-9ba0-8d7ee481b9bd" xlink:to="loc_us-gaap_TradeNamesMember_23b03a98-d41b-4e8d-aedd-ac9f9da8def3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/RestructuringActivitiesNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#RestructuringActivitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/RestructuringActivitiesNarrativeDetails" xlink:type="extended" id="i2c10cc49768d4fbe9cb3c801f7670b6c_RestructuringActivitiesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_a7eecfc1-da4f-438a-b836-b2e352bcb762" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_98342e48-e833-43aa-b9bc-df0c1b58e1aa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_a7eecfc1-da4f-438a-b836-b2e352bcb762" xlink:to="loc_us-gaap_RestructuringCharges_98342e48-e833-43aa-b9bc-df0c1b58e1aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_2cc249d4-e87c-4920-82d4-0588ecf2d705" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_a7eecfc1-da4f-438a-b836-b2e352bcb762" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_2cc249d4-e87c-4920-82d4-0588ecf2d705" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_6407476e-47a4-4910-889e-3d3edd44f25d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_a7eecfc1-da4f-438a-b836-b2e352bcb762" xlink:to="loc_us-gaap_RestructuringReserve_6407476e-47a4-4910-889e-3d3edd44f25d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_aaf1ebe5-6cab-48b7-aff8-f1c519e31a20" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_a7eecfc1-da4f-438a-b836-b2e352bcb762" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_aaf1ebe5-6cab-48b7-aff8-f1c519e31a20" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_c848fb64-171d-4865-b304-a3c7d6b41010" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_aaf1ebe5-6cab-48b7-aff8-f1c519e31a20" xlink:to="loc_us-gaap_RestructuringPlanAxis_c848fb64-171d-4865-b304-a3c7d6b41010" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_c848fb64-171d-4865-b304-a3c7d6b41010_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_c848fb64-171d-4865-b304-a3c7d6b41010" xlink:to="loc_us-gaap_RestructuringPlanDomain_c848fb64-171d-4865-b304-a3c7d6b41010_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_e855c1e2-01ef-4f9c-87ec-478e6519ea42" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_c848fb64-171d-4865-b304-a3c7d6b41010" xlink:to="loc_us-gaap_RestructuringPlanDomain_e855c1e2-01ef-4f9c-87ec-478e6519ea42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_RestructuringPlan2022Member_91fb10bc-e16b-4207-9704-cc539fcc8a51" xlink:href="dco-20221231.xsd#dco_RestructuringPlan2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_e855c1e2-01ef-4f9c-87ec-478e6519ea42" xlink:to="loc_dco_RestructuringPlan2022Member_91fb10bc-e16b-4207-9704-cc539fcc8a51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_6f72014c-044e-4fc5-bde3-8d38c5dd88c1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_aaf1ebe5-6cab-48b7-aff8-f1c519e31a20" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_6f72014c-044e-4fc5-bde3-8d38c5dd88c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_6f72014c-044e-4fc5-bde3-8d38c5dd88c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_6f72014c-044e-4fc5-bde3-8d38c5dd88c1" xlink:to="loc_us-gaap_SegmentDomain_6f72014c-044e-4fc5-bde3-8d38c5dd88c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_04368485-de59-4090-8818-382fc6a53f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_6f72014c-044e-4fc5-bde3-8d38c5dd88c1" xlink:to="loc_us-gaap_SegmentDomain_04368485-de59-4090-8818-382fc6a53f8c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_b3358e73-64c5-4299-801a-bbaf5c3c2dd9" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_04368485-de59-4090-8818-382fc6a53f8c" xlink:to="loc_dco_ElectronicSystemsSegmentMember_b3358e73-64c5-4299-801a-bbaf5c3c2dd9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_36e63386-c0b8-4480-a8eb-9db017d0a421" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_04368485-de59-4090-8818-382fc6a53f8c" xlink:to="loc_dco_StructuralSystemsSegmentMember_36e63386-c0b8-4480-a8eb-9db017d0a421" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_458ff1ee-6496-4697-9ac2-c13aed4cd3b7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_aaf1ebe5-6cab-48b7-aff8-f1c519e31a20" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_458ff1ee-6496-4697-9ac2-c13aed4cd3b7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_458ff1ee-6496-4697-9ac2-c13aed4cd3b7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_458ff1ee-6496-4697-9ac2-c13aed4cd3b7" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_458ff1ee-6496-4697-9ac2-c13aed4cd3b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_bb0cbab2-ac4c-4d68-9252-77e3d4e4f24e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_458ff1ee-6496-4697-9ac2-c13aed4cd3b7" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_bb0cbab2-ac4c-4d68-9252-77e3d4e4f24e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_7dbaaa0a-bd07-49eb-956a-10698afb8c13" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_bb0cbab2-ac4c-4d68-9252-77e3d4e4f24e" xlink:to="loc_us-gaap_EmployeeSeveranceMember_7dbaaa0a-bd07-49eb-956a-10698afb8c13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyAndEquipmentImpairmentMember_1f199555-405f-4615-92ca-38c0519bc3c1" xlink:href="dco-20221231.xsd#dco_PropertyAndEquipmentImpairmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_bb0cbab2-ac4c-4d68-9252-77e3d4e4f24e" xlink:to="loc_dco_PropertyAndEquipmentImpairmentMember_1f199555-405f-4615-92ca-38c0519bc3c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_29c5aed7-6b42-4dde-aaac-7a357c5368bd" xlink:href="dco-20221231.xsd#dco_PropertyAndEquipmentAcceleratedDepreciationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_bb0cbab2-ac4c-4d68-9252-77e3d4e4f24e" xlink:to="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_29c5aed7-6b42-4dde-aaac-7a357c5368bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_InventoryWriteDownMember_a879da1c-1ee4-4621-83b7-ffbaae51e024" xlink:href="dco-20221231.xsd#dco_InventoryWriteDownMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_bb0cbab2-ac4c-4d68-9252-77e3d4e4f24e" xlink:to="loc_dco_InventoryWriteDownMember_a879da1c-1ee4-4621-83b7-ffbaae51e024" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_986c0de0-b0bf-47a5-ad34-bb98ee9aaa8d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_aaf1ebe5-6cab-48b7-aff8-f1c519e31a20" xlink:to="loc_srt_RangeAxis_986c0de0-b0bf-47a5-ad34-bb98ee9aaa8d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_986c0de0-b0bf-47a5-ad34-bb98ee9aaa8d_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_986c0de0-b0bf-47a5-ad34-bb98ee9aaa8d" xlink:to="loc_srt_RangeMember_986c0de0-b0bf-47a5-ad34-bb98ee9aaa8d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5dcf0599-67c5-4b37-813c-2de98be8e068" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_986c0de0-b0bf-47a5-ad34-bb98ee9aaa8d" xlink:to="loc_srt_RangeMember_5dcf0599-67c5-4b37-813c-2de98be8e068" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c36a138a-8817-41b8-b836-927abf935f87" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_5dcf0599-67c5-4b37-813c-2de98be8e068" xlink:to="loc_srt_MinimumMember_c36a138a-8817-41b8-b836-927abf935f87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_9afbd66b-a800-4c0b-a837-61ae0eb29f68" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_5dcf0599-67c5-4b37-813c-2de98be8e068" xlink:to="loc_srt_MaximumMember_9afbd66b-a800-4c0b-a837-61ae0eb29f68" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/RestructuringActivitiesDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#RestructuringActivitiesDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/RestructuringActivitiesDetails" xlink:type="extended" id="i7508a468c4e64346a6785b99ca560693_RestructuringActivitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_452af812-8dcb-449d-a9b3-873ed98554aa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_7a5a0572-8f52-4898-a20b-e617836abf29" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_452af812-8dcb-449d-a9b3-873ed98554aa" xlink:to="loc_us-gaap_RestructuringReserveRollForward_7a5a0572-8f52-4898-a20b-e617836abf29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_9ac6d2d1-c251-4f95-b154-cc6376b516d3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_7a5a0572-8f52-4898-a20b-e617836abf29" xlink:to="loc_us-gaap_RestructuringReserve_9ac6d2d1-c251-4f95-b154-cc6376b516d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_6468dfa2-f084-40a2-8d05-776c3a0dc9b3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_7a5a0572-8f52-4898-a20b-e617836abf29" xlink:to="loc_us-gaap_RestructuringCharges_6468dfa2-f084-40a2-8d05-776c3a0dc9b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_352fbd92-268e-4cd4-8713-abf4d57c961c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_7a5a0572-8f52-4898-a20b-e617836abf29" xlink:to="loc_us-gaap_PaymentsForRestructuring_352fbd92-268e-4cd4-8713-abf4d57c961c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveSettledWithoutCash2_cef78a40-17b0-4571-b9e3-a50446b23337" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserveSettledWithoutCash2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_7a5a0572-8f52-4898-a20b-e617836abf29" xlink:to="loc_us-gaap_RestructuringReserveSettledWithoutCash2_cef78a40-17b0-4571-b9e3-a50446b23337" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAccrualAdjustment1_0b6ccbf2-b7d5-4aa6-a121-6f2f224cfc9c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserveAccrualAdjustment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_7a5a0572-8f52-4898-a20b-e617836abf29" xlink:to="loc_us-gaap_RestructuringReserveAccrualAdjustment1_0b6ccbf2-b7d5-4aa6-a121-6f2f224cfc9c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_0467c049-49e1-4d17-a614-a5759fc8d387" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringReserve"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ebe10145-e64b-46d3-86aa-e4077f3c3f03" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_452af812-8dcb-449d-a9b3-873ed98554aa" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ebe10145-e64b-46d3-86aa-e4077f3c3f03" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_ef13ff16-b1bb-4e40-b64f-f417c253d15d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ebe10145-e64b-46d3-86aa-e4077f3c3f03" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_ef13ff16-b1bb-4e40-b64f-f417c253d15d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_ef13ff16-b1bb-4e40-b64f-f417c253d15d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_ef13ff16-b1bb-4e40-b64f-f417c253d15d" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_ef13ff16-b1bb-4e40-b64f-f417c253d15d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_320da85c-7320-45bd-9b1a-e4b00083fb6c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_ef13ff16-b1bb-4e40-b64f-f417c253d15d" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_320da85c-7320-45bd-9b1a-e4b00083fb6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_7c92d839-4ade-48ed-83b7-bea0dcf63ca2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_320da85c-7320-45bd-9b1a-e4b00083fb6c" xlink:to="loc_us-gaap_EmployeeSeveranceMember_7c92d839-4ade-48ed-83b7-bea0dcf63ca2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_df312810-26c9-4fde-9984-ca8349983928" xlink:href="dco-20221231.xsd#dco_PropertyAndEquipmentAcceleratedDepreciationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_320da85c-7320-45bd-9b1a-e4b00083fb6c" xlink:to="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_df312810-26c9-4fde-9984-ca8349983928" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyAndEquipmentImpairmentMember_ad5b22c6-b089-47d6-b1f9-51be0c87b261" xlink:href="dco-20221231.xsd#dco_PropertyAndEquipmentImpairmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_320da85c-7320-45bd-9b1a-e4b00083fb6c" xlink:to="loc_dco_PropertyAndEquipmentImpairmentMember_ad5b22c6-b089-47d6-b1f9-51be0c87b261" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_InventoryWriteDownMember_77b66ad2-a88b-463a-9695-d80261d44705" xlink:href="dco-20221231.xsd#dco_InventoryWriteDownMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_320da85c-7320-45bd-9b1a-e4b00083fb6c" xlink:to="loc_dco_InventoryWriteDownMember_77b66ad2-a88b-463a-9695-d80261d44705" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_d3c8541b-fb8e-4568-8b7b-35fa39709000" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_ebe10145-e64b-46d3-86aa-e4077f3c3f03" xlink:to="loc_us-gaap_RestructuringPlanAxis_d3c8541b-fb8e-4568-8b7b-35fa39709000" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_d3c8541b-fb8e-4568-8b7b-35fa39709000_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_d3c8541b-fb8e-4568-8b7b-35fa39709000" xlink:to="loc_us-gaap_RestructuringPlanDomain_d3c8541b-fb8e-4568-8b7b-35fa39709000_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_b78d53bb-82e6-4630-a3a2-1f2df085efd5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_d3c8541b-fb8e-4568-8b7b-35fa39709000" xlink:to="loc_us-gaap_RestructuringPlanDomain_b78d53bb-82e6-4630-a3a2-1f2df085efd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_RestructuringPlan2022Member_e020a759-256f-4d55-a6c3-ecc437f9e45d" xlink:href="dco-20221231.xsd#dco_RestructuringPlan2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_b78d53bb-82e6-4630-a3a2-1f2df085efd5" xlink:to="loc_dco_RestructuringPlan2022Member_e020a759-256f-4d55-a6c3-ecc437f9e45d" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/PropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#PropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/PropertyandEquipmentNetDetails" xlink:type="extended" id="i061c2a690e7f4bb0b257f00bca57accc_PropertyandEquipmentNetDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_90ea6aeb-c54e-400e-89ce-8e043a3c4bf0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_139d1921-4767-4b8f-8a61-9ab3e12ee469" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_90ea6aeb-c54e-400e-89ce-8e043a3c4bf0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_139d1921-4767-4b8f-8a61-9ab3e12ee469" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_a1def5a1-5c08-4e95-9066-c5b5b149ca92" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_90ea6aeb-c54e-400e-89ce-8e043a3c4bf0" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_a1def5a1-5c08-4e95-9066-c5b5b149ca92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_804481db-4a42-49c1-9171-73c1534f41c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_90ea6aeb-c54e-400e-89ce-8e043a3c4bf0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_804481db-4a42-49c1-9171-73c1534f41c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_807d23d8-de8b-49db-b9c2-e09ed0dbb391" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_90ea6aeb-c54e-400e-89ce-8e043a3c4bf0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_807d23d8-de8b-49db-b9c2-e09ed0dbb391" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_412d1c1f-0935-4a57-9afd-456c756318b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_90ea6aeb-c54e-400e-89ce-8e043a3c4bf0" xlink:to="loc_us-gaap_Depreciation_412d1c1f-0935-4a57-9afd-456c756318b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fc392208-803c-4370-9706-dd496856350c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_90ea6aeb-c54e-400e-89ce-8e043a3c4bf0" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fc392208-803c-4370-9706-dd496856350c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6a730a2-aaa4-4f81-9f87-3c8561d6a7ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fc392208-803c-4370-9706-dd496856350c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6a730a2-aaa4-4f81-9f87-3c8561d6a7ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d6a730a2-aaa4-4f81-9f87-3c8561d6a7ae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6a730a2-aaa4-4f81-9f87-3c8561d6a7ae" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d6a730a2-aaa4-4f81-9f87-3c8561d6a7ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6eac9353-84ef-43e8-8be9-1f16acaba778" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6a730a2-aaa4-4f81-9f87-3c8561d6a7ae" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6eac9353-84ef-43e8-8be9-1f16acaba778" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_a93778b7-33d2-4004-b625-0d3b6834c012" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6eac9353-84ef-43e8-8be9-1f16acaba778" xlink:to="loc_us-gaap_LandMember_a93778b7-33d2-4004-b625-0d3b6834c012" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_008231b1-5509-4478-81f4-bff2d381abb9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6eac9353-84ef-43e8-8be9-1f16acaba778" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_008231b1-5509-4478-81f4-bff2d381abb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_40a757c1-48fe-4284-be66-65c37435c92b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6eac9353-84ef-43e8-8be9-1f16acaba778" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_40a757c1-48fe-4284-be66-65c37435c92b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_9599381a-60ab-45ea-8caf-99062bdc05d4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6eac9353-84ef-43e8-8be9-1f16acaba778" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_9599381a-60ab-45ea-8caf-99062bdc05d4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_a45a1b82-4531-4153-abcb-2cb7375451e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6eac9353-84ef-43e8-8be9-1f16acaba778" xlink:to="loc_us-gaap_ConstructionInProgressMember_a45a1b82-4531-4153-abcb-2cb7375451e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_7559cefb-9f3d-4204-b437-634bdc071fc3" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fc392208-803c-4370-9706-dd496856350c" xlink:to="loc_srt_RangeAxis_7559cefb-9f3d-4204-b437-634bdc071fc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_7559cefb-9f3d-4204-b437-634bdc071fc3_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_7559cefb-9f3d-4204-b437-634bdc071fc3" xlink:to="loc_srt_RangeMember_7559cefb-9f3d-4204-b437-634bdc071fc3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5954b8e5-81d8-4caa-afd7-0e99e84e9e72" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_7559cefb-9f3d-4204-b437-634bdc071fc3" xlink:to="loc_srt_RangeMember_5954b8e5-81d8-4caa-afd7-0e99e84e9e72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_b06b7a68-3f9f-4e26-8569-fb5358769b98" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_5954b8e5-81d8-4caa-afd7-0e99e84e9e72" xlink:to="loc_srt_MinimumMember_b06b7a68-3f9f-4e26-8569-fb5358769b98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_27cc1a99-d144-47f0-9906-aa49f7f04005" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_5954b8e5-81d8-4caa-afd7-0e99e84e9e72" xlink:to="loc_srt_MaximumMember_27cc1a99-d144-47f0-9906-aa49f7f04005" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/LeasesNarrativeDetails" xlink:type="extended" id="i3c885e344bf14abbab0efc3b4db3ab1a_LeasesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLeasePaymentSalesTypeAndDirectFinancingLeasesInvestingActivity_92f2c07d-5d4b-427d-a967-4a3be00a4019" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromLeasePaymentSalesTypeAndDirectFinancingLeasesInvestingActivity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_us-gaap_ProceedsFromLeasePaymentSalesTypeAndDirectFinancingLeasesInvestingActivity_92f2c07d-5d4b-427d-a967-4a3be00a4019" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleLeasebackTransactionNetBookValue_047308c6-79dc-4046-88ea-17f34c400527" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleLeasebackTransactionNetBookValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_us-gaap_SaleLeasebackTransactionNetBookValue_047308c6-79dc-4046-88ea-17f34c400527" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleAndLeasebackTransactionGainLossNet_c2dc8efd-9d6f-4671-8877-5b1130960575" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SaleAndLeasebackTransactionGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_us-gaap_SaleAndLeasebackTransactionGainLossNet_c2dc8efd-9d6f-4671-8877-5b1130960575" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SaleLeasebackTransactionLeaseContractTerms_859332db-477b-4e5b-93b1-64fa0d963810" xlink:href="dco-20221231.xsd#dco_SaleLeasebackTransactionLeaseContractTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_SaleLeasebackTransactionLeaseContractTerms_859332db-477b-4e5b-93b1-64fa0d963810" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SaleLeasebackTransactionLeaseRenewOption_d19e0b20-5be0-4224-8eda-26a323e70b2d" xlink:href="dco-20221231.xsd#dco_SaleLeasebackTransactionLeaseRenewOption"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_SaleLeasebackTransactionLeaseRenewOption_d19e0b20-5be0-4224-8eda-26a323e70b2d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SaleLeasebackTransactionAggregateMinimumMonthlyLeasePayments_7a6eb8c2-b17f-4d5a-8f88-1bb6ec02682b" xlink:href="dco-20221231.xsd#dco_SaleLeasebackTransactionAggregateMinimumMonthlyLeasePayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_SaleLeasebackTransactionAggregateMinimumMonthlyLeasePayments_7a6eb8c2-b17f-4d5a-8f88-1bb6ec02682b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LeaseRemainingLeaseTerm_6368fa8f-a939-48ac-b1a7-b8415ee5d1d4" xlink:href="dco-20221231.xsd#dco_LeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_LeaseRemainingLeaseTerm_6368fa8f-a939-48ac-b1a7-b8415ee5d1d4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LesseeLeaseRenewalTerm_bf9ee6ca-ac4e-437e-a4ce-fb8379c1e79e" xlink:href="dco-20221231.xsd#dco_LesseeLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_LesseeLeaseRenewalTerm_bf9ee6ca-ac4e-437e-a4ce-fb8379c1e79e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LesseeLeaseTerminationPeriod_a344d62c-c00e-483f-b4e6-53ce5542394c" xlink:href="dco-20221231.xsd#dco_LesseeLeaseTerminationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_LesseeLeaseTerminationPeriod_a344d62c-c00e-483f-b4e6-53ce5542394c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LesseeOperatingLeaseLiabilityPaymentsDueWithOptionToExtend_76154c04-a076-4c71-8237-9e369046c394" xlink:href="dco-20221231.xsd#dco_LesseeOperatingLeaseLiabilityPaymentsDueWithOptionToExtend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_LesseeOperatingLeaseLiabilityPaymentsDueWithOptionToExtend_76154c04-a076-4c71-8237-9e369046c394" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LesseeOperatingLeaseLeaseNotYetCommencedAmount_9216df8d-8f51-478f-ba00-a1f5f0c72375" xlink:href="dco-20221231.xsd#dco_LesseeOperatingLeaseLeaseNotYetCommencedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_LesseeOperatingLeaseLeaseNotYetCommencedAmount_9216df8d-8f51-478f-ba00-a1f5f0c72375" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LesseeFinanceLeaseLeaseNotYetCommencedAmount_2fa0b6b2-3021-4cd0-9e9d-1c317f14d230" xlink:href="dco-20221231.xsd#dco_LesseeFinanceLeaseLeaseNotYetCommencedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_dco_LesseeFinanceLeaseLeaseNotYetCommencedAmount_2fa0b6b2-3021-4cd0-9e9d-1c317f14d230" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_f6ed9a29-d7d2-4d60-830f-fe11e7834f21" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_3ef03052-33ac-4e6f-9bb1-bd41c7443819" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_f6ed9a29-d7d2-4d60-830f-fe11e7834f21" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_76da5620-24ab-444d-9f7b-8a013b1ce80f" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_f6ed9a29-d7d2-4d60-830f-fe11e7834f21" xlink:to="loc_srt_RangeAxis_76da5620-24ab-444d-9f7b-8a013b1ce80f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_76da5620-24ab-444d-9f7b-8a013b1ce80f_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_76da5620-24ab-444d-9f7b-8a013b1ce80f" xlink:to="loc_srt_RangeMember_76da5620-24ab-444d-9f7b-8a013b1ce80f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0fb02b07-8522-47cc-ba36-0bd40ffbb001" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_76da5620-24ab-444d-9f7b-8a013b1ce80f" xlink:to="loc_srt_RangeMember_0fb02b07-8522-47cc-ba36-0bd40ffbb001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_f499358e-2bf4-43dc-bf21-398495fa0b63" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_0fb02b07-8522-47cc-ba36-0bd40ffbb001" xlink:to="loc_srt_MinimumMember_f499358e-2bf4-43dc-bf21-398495fa0b63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_e9e2b32d-b9db-4f2d-944f-fd44a86a3c53" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_0fb02b07-8522-47cc-ba36-0bd40ffbb001" xlink:to="loc_srt_MaximumMember_e9e2b32d-b9db-4f2d-944f-fd44a86a3c53" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsCarryingAmountofGoodwillDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#GoodwillandOtherIntangibleAssetsCarryingAmountofGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsCarryingAmountofGoodwillDetails" xlink:type="extended" id="i9754a63d984a48a399f1ff1847fb57bc_GoodwillandOtherIntangibleAssetsCarryingAmountofGoodwillDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_776cd883-84d8-4a71-b211-c08b9436fc40" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillGross_b5f61a8c-cdd5-446d-8cfb-125bb00410d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_776cd883-84d8-4a71-b211-c08b9436fc40" xlink:to="loc_us-gaap_GoodwillGross_b5f61a8c-cdd5-446d-8cfb-125bb00410d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_7b65a509-1c20-4b12-ae6c-420d40a402e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_776cd883-84d8-4a71-b211-c08b9436fc40" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_7b65a509-1c20-4b12-ae6c-420d40a402e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_ed3447e4-cb2b-4027-a3ed-806402ef2127" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_776cd883-84d8-4a71-b211-c08b9436fc40" xlink:to="loc_us-gaap_GoodwillRollForward_ed3447e4-cb2b-4027-a3ed-806402ef2127" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_afd0ba1a-111f-4840-8554-2d7fd9433f10" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_ed3447e4-cb2b-4027-a3ed-806402ef2127" xlink:to="loc_us-gaap_Goodwill_afd0ba1a-111f-4840-8554-2d7fd9433f10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_bfab9b2b-61fb-48d1-927d-3862b8b58257" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_ed3447e4-cb2b-4027-a3ed-806402ef2127" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_bfab9b2b-61fb-48d1-927d-3862b8b58257" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_7b75a7f1-65c8-453b-b365-67272c48a5e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_ffa6ff20-f6c9-4981-a05c-283239231d93" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_776cd883-84d8-4a71-b211-c08b9436fc40" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_ffa6ff20-f6c9-4981-a05c-283239231d93" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_5e0e0fa6-3ecc-49ff-9cbb-56a25c1cc988" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_ffa6ff20-f6c9-4981-a05c-283239231d93" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_5e0e0fa6-3ecc-49ff-9cbb-56a25c1cc988" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_5e0e0fa6-3ecc-49ff-9cbb-56a25c1cc988_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5e0e0fa6-3ecc-49ff-9cbb-56a25c1cc988" xlink:to="loc_us-gaap_SegmentDomain_5e0e0fa6-3ecc-49ff-9cbb-56a25c1cc988_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b077bfdf-1ed3-45b6-897b-9d39b8a6ba3d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5e0e0fa6-3ecc-49ff-9cbb-56a25c1cc988" xlink:to="loc_us-gaap_SegmentDomain_b077bfdf-1ed3-45b6-897b-9d39b8a6ba3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_f02a6a67-dc11-401f-bde3-0f2a132f0e9c" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_b077bfdf-1ed3-45b6-897b-9d39b8a6ba3d" xlink:to="loc_dco_ElectronicSystemsSegmentMember_f02a6a67-dc11-401f-bde3-0f2a132f0e9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_67389317-b4a2-4d36-b9ef-151485106b92" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_b077bfdf-1ed3-45b6-897b-9d39b8a6ba3d" xlink:to="loc_dco_StructuralSystemsSegmentMember_67389317-b4a2-4d36-b9ef-151485106b92" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#GoodwillandOtherIntangibleAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails" xlink:type="extended" id="icb7aae46d56d499486a0bd2fdc3b6815_GoodwillandOtherIntangibleAssetsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_dco_GoodwillAndIntangibleAssetsLineItems_31bc8e0a-a82c-413f-bb72-5338707406b6" xlink:href="dco-20221231.xsd#dco_GoodwillAndIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_a36793c3-de84-4a63-ae86-eca7e4b2c64c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_GoodwillAndIntangibleAssetsLineItems_31bc8e0a-a82c-413f-bb72-5338707406b6" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_a36793c3-de84-4a63-ae86-eca7e4b2c64c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_dcb8a7e1-f629-4565-acc8-0408560251d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_GoodwillAndIntangibleAssetsLineItems_31bc8e0a-a82c-413f-bb72-5338707406b6" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_dcb8a7e1-f629-4565-acc8-0408560251d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_d076b7be-5ae1-44b8-a038-d6ca9c843e8e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_GoodwillAndIntangibleAssetsLineItems_31bc8e0a-a82c-413f-bb72-5338707406b6" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_d076b7be-5ae1-44b8-a038-d6ca9c843e8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_5d678d2e-3ca4-4e36-885c-17f2d1b1e9e6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_GoodwillAndIntangibleAssetsLineItems_31bc8e0a-a82c-413f-bb72-5338707406b6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_5d678d2e-3ca4-4e36-885c-17f2d1b1e9e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_8a944988-f1d1-4bb8-9467-d0ce0fd61438" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_GoodwillAndIntangibleAssetsLineItems_31bc8e0a-a82c-413f-bb72-5338707406b6" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_8a944988-f1d1-4bb8-9467-d0ce0fd61438" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GoodwillAndIntangibleAssetsTable_a20e7733-581e-4f30-b8d5-37223fd85d8d" xlink:href="dco-20221231.xsd#dco_GoodwillAndIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dco_GoodwillAndIntangibleAssetsLineItems_31bc8e0a-a82c-413f-bb72-5338707406b6" xlink:to="loc_dco_GoodwillAndIntangibleAssetsTable_a20e7733-581e-4f30-b8d5-37223fd85d8d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_94dae670-8d58-436c-80c6-9fc8f04b45ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_GoodwillAndIntangibleAssetsTable_a20e7733-581e-4f30-b8d5-37223fd85d8d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_94dae670-8d58-436c-80c6-9fc8f04b45ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_94dae670-8d58-436c-80c6-9fc8f04b45ef_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_94dae670-8d58-436c-80c6-9fc8f04b45ef" xlink:to="loc_us-gaap_SegmentDomain_94dae670-8d58-436c-80c6-9fc8f04b45ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8930457b-38d5-4ed2-8c40-c2d75c5a295e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_94dae670-8d58-436c-80c6-9fc8f04b45ef" xlink:to="loc_us-gaap_SegmentDomain_8930457b-38d5-4ed2-8c40-c2d75c5a295e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_84342259-093d-4256-8cf3-b19b14419eab" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8930457b-38d5-4ed2-8c40-c2d75c5a295e" xlink:to="loc_dco_ElectronicSystemsSegmentMember_84342259-093d-4256-8cf3-b19b14419eab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_ec5287d6-8523-4b72-8168-c978509a49a9" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8930457b-38d5-4ed2-8c40-c2d75c5a295e" xlink:to="loc_dco_StructuralSystemsSegmentMember_ec5287d6-8523-4b72-8168-c978509a49a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_f585c302-3977-4e04-bbf9-78064bf7683e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_GoodwillAndIntangibleAssetsTable_a20e7733-581e-4f30-b8d5-37223fd85d8d" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_f585c302-3977-4e04-bbf9-78064bf7683e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f585c302-3977-4e04-bbf9-78064bf7683e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_f585c302-3977-4e04-bbf9-78064bf7683e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_f585c302-3977-4e04-bbf9-78064bf7683e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_768bbd2e-cc80-4ee6-bd2a-6c1abdb543c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_f585c302-3977-4e04-bbf9-78064bf7683e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_768bbd2e-cc80-4ee6-bd2a-6c1abdb543c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_dc93b7d0-ff78-4419-8823-4dac5c492cbc" xlink:href="dco-20221231.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_768bbd2e-cc80-4ee6-bd2a-6c1abdb543c2" xlink:to="loc_dco_MagneticSealCorporationMember_dc93b7d0-ff78-4419-8823-4dac5c492cbc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_5e4c6688-a823-449b-b554-737432f9b627" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_GoodwillAndIntangibleAssetsTable_a20e7733-581e-4f30-b8d5-37223fd85d8d" xlink:to="loc_srt_RangeAxis_5e4c6688-a823-449b-b554-737432f9b627" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5e4c6688-a823-449b-b554-737432f9b627_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_5e4c6688-a823-449b-b554-737432f9b627" xlink:to="loc_srt_RangeMember_5e4c6688-a823-449b-b554-737432f9b627_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2fded71d-c249-4d23-aaa5-0f7860a387ed" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_5e4c6688-a823-449b-b554-737432f9b627" xlink:to="loc_srt_RangeMember_2fded71d-c249-4d23-aaa5-0f7860a387ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_d96467ab-d509-4f2b-865d-22400b6e2ff1" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2fded71d-c249-4d23-aaa5-0f7860a387ed" xlink:to="loc_srt_MinimumMember_d96467ab-d509-4f2b-865d-22400b6e2ff1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_36f3f11a-0fe6-4fd8-b64c-7db9861da3cf" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2fded71d-c249-4d23-aaa5-0f7860a387ed" xlink:to="loc_srt_MaximumMember_36f3f11a-0fe6-4fd8-b64c-7db9861da3cf" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsCarryingAmountofFinitelivedandOtherIntangibleAssetsDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#GoodwillandOtherIntangibleAssetsCarryingAmountofFinitelivedandOtherIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsCarryingAmountofFinitelivedandOtherIntangibleAssetsDetails" xlink:type="extended" id="i3dfe15183cac4dbab6a0b0426231d1d7_GoodwillandOtherIntangibleAssetsCarryingAmountofFinitelivedandOtherIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6baeb457-c71e-4a2d-95aa-f9423bfcdde2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_a1a97418-35b5-494c-bcdc-90627794a14b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6baeb457-c71e-4a2d-95aa-f9423bfcdde2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_a1a97418-35b5-494c-bcdc-90627794a14b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_175984db-b39e-4fc5-8985-a26eef3bc330" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6baeb457-c71e-4a2d-95aa-f9423bfcdde2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_175984db-b39e-4fc5-8985-a26eef3bc330" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_421eadd5-fe57-48b1-81af-6951b0e9e552" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_175984db-b39e-4fc5-8985-a26eef3bc330" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_421eadd5-fe57-48b1-81af-6951b0e9e552" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_5aaf9760-bd29-4519-a377-4522cfc1fca3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_175984db-b39e-4fc5-8985-a26eef3bc330" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_5aaf9760-bd29-4519-a377-4522cfc1fca3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_f9843233-21c6-4f75-927b-0f2f8cdb2f27" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_175984db-b39e-4fc5-8985-a26eef3bc330" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_f9843233-21c6-4f75-927b-0f2f8cdb2f27" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_IndefiniteLivedAssetsAbstract_fe51f112-dcdc-41cc-85dc-4f0c0a84a307" xlink:href="dco-20221231.xsd#dco_IndefiniteLivedAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6baeb457-c71e-4a2d-95aa-f9423bfcdde2" xlink:to="loc_dco_IndefiniteLivedAssetsAbstract_fe51f112-dcdc-41cc-85dc-4f0c0a84a307" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_791d234c-c84f-439a-a32a-9b9c084b468f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_IndefiniteLivedAssetsAbstract_fe51f112-dcdc-41cc-85dc-4f0c0a84a307" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_791d234c-c84f-439a-a32a-9b9c084b468f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_23f34352-ee90-49f2-a481-d3da9d4fd21c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6baeb457-c71e-4a2d-95aa-f9423bfcdde2" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_23f34352-ee90-49f2-a481-d3da9d4fd21c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_98cd1b3d-6b1a-48d3-8167-18829aa94747" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6baeb457-c71e-4a2d-95aa-f9423bfcdde2" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_98cd1b3d-6b1a-48d3-8167-18829aa94747" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_41e37b8a-454b-458e-978d-cd1ea640a486" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_6baeb457-c71e-4a2d-95aa-f9423bfcdde2" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_41e37b8a-454b-458e-978d-cd1ea640a486" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee7dbd82-1822-41b1-b851-2106e19662c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_41e37b8a-454b-458e-978d-cd1ea640a486" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee7dbd82-1822-41b1-b851-2106e19662c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ee7dbd82-1822-41b1-b851-2106e19662c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee7dbd82-1822-41b1-b851-2106e19662c9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ee7dbd82-1822-41b1-b851-2106e19662c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c0b4905-2f3e-496a-b7c9-37383d118354" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_ee7dbd82-1822-41b1-b851-2106e19662c9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c0b4905-2f3e-496a-b7c9-37383d118354" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_5ec9d9ab-6a11-4f8b-be2f-f15fcc1d5c02" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c0b4905-2f3e-496a-b7c9-37383d118354" xlink:to="loc_us-gaap_CustomerRelationshipsMember_5ec9d9ab-6a11-4f8b-be2f-f15fcc1d5c02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_2b1a4281-44d2-41f4-8148-86902aa5dcc2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c0b4905-2f3e-496a-b7c9-37383d118354" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_2b1a4281-44d2-41f4-8148-86902aa5dcc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ContractRenewalMember_b368750b-4e5d-4741-9610-20d3a157de58" xlink:href="dco-20221231.xsd#dco_ContractRenewalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c0b4905-2f3e-496a-b7c9-37383d118354" xlink:to="loc_dco_ContractRenewalMember_b368750b-4e5d-4741-9610-20d3a157de58" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_TechnologyMember_62c6f860-380c-4291-9a18-7d3dad0d7ec8" xlink:href="dco-20221231.xsd#dco_TechnologyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c0b4905-2f3e-496a-b7c9-37383d118354" xlink:to="loc_dco_TechnologyMember_62c6f860-380c-4291-9a18-7d3dad0d7ec8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OrderOrProductionBacklogMember_2ca30ef4-d473-4ae9-b8ee-2c4e7cbc50b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OrderOrProductionBacklogMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_3c0b4905-2f3e-496a-b7c9-37383d118354" xlink:to="loc_us-gaap_OrderOrProductionBacklogMember_2ca30ef4-d473-4ae9-b8ee-2c4e7cbc50b6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_b73ad924-1d0e-4a68-8aba-4221b8b9ab1c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_41e37b8a-454b-458e-978d-cd1ea640a486" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_b73ad924-1d0e-4a68-8aba-4221b8b9ab1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b73ad924-1d0e-4a68-8aba-4221b8b9ab1c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b73ad924-1d0e-4a68-8aba-4221b8b9ab1c" xlink:to="loc_us-gaap_SegmentDomain_b73ad924-1d0e-4a68-8aba-4221b8b9ab1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_866f95fb-2065-4bc4-99ba-9e25edb30207" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b73ad924-1d0e-4a68-8aba-4221b8b9ab1c" xlink:to="loc_us-gaap_SegmentDomain_866f95fb-2065-4bc4-99ba-9e25edb30207" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_1d7b2673-fd11-4abc-81dc-c052c5180d86" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_866f95fb-2065-4bc4-99ba-9e25edb30207" xlink:to="loc_dco_ElectronicSystemsSegmentMember_1d7b2673-fd11-4abc-81dc-c052c5180d86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_4fb06bb6-54a8-4612-9a81-e4eebb29db81" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_866f95fb-2065-4bc4-99ba-9e25edb30207" xlink:to="loc_dco_StructuralSystemsSegmentMember_4fb06bb6-54a8-4612-9a81-e4eebb29db81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_57855ced-9804-48cd-8ba3-c257e69f84c8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_41e37b8a-454b-458e-978d-cd1ea640a486" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_57855ced-9804-48cd-8ba3-c257e69f84c8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_57855ced-9804-48cd-8ba3-c257e69f84c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_57855ced-9804-48cd-8ba3-c257e69f84c8" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_57855ced-9804-48cd-8ba3-c257e69f84c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_ca89044b-0968-4c54-9a86-1d56ee90b1cb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_57855ced-9804-48cd-8ba3-c257e69f84c8" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_ca89044b-0968-4c54-9a86-1d56ee90b1cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_cee9f7a9-25e3-4dd2-9129-25257a2547dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_ca89044b-0968-4c54-9a86-1d56ee90b1cb" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_cee9f7a9-25e3-4dd2-9129-25257a2547dc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsFutureAmortizationExpenseofOtherIntangibleAssetsDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#GoodwillandOtherIntangibleAssetsFutureAmortizationExpenseofOtherIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/GoodwillandOtherIntangibleAssetsFutureAmortizationExpenseofOtherIntangibleAssetsDetails" xlink:type="extended" id="ied8919643a86486c87f71a06163a866a_GoodwillandOtherIntangibleAssetsFutureAmortizationExpenseofOtherIntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_5a4cb3e9-95e5-4a88-9bf4-cde4cf09f145" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_5a4cb3e9-95e5-4a88-9bf4-cde4cf09f145" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_e3ea1774-30b8-461e-9a68-f8931c0fb0d3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_e3ea1774-30b8-461e-9a68-f8931c0fb0d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_7e66be4d-aacc-4d15-b166-aa0f35656b1a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_7e66be4d-aacc-4d15-b166-aa0f35656b1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_a412f2a5-cc7d-46b2-8a20-a57eafb44621" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_a412f2a5-cc7d-46b2-8a20-a57eafb44621" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_ca94c2e8-fa28-491e-9ee4-bcb163092b46" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_ca94c2e8-fa28-491e-9ee4-bcb163092b46" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_7d68c495-207e-43b4-a074-b4586fc16d6d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_7d68c495-207e-43b4-a074-b4586fc16d6d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_cf12c91a-606b-4911-a652-61dc100c2f05" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_cf12c91a-606b-4911-a652-61dc100c2f05" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_74f66b03-3c5b-45a7-961a-b7ef3aa3d1c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_bc46042a-27d1-45d9-b075-b0cd1c75f94f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_74f66b03-3c5b-45a7-961a-b7ef3aa3d1c6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_6f7d866e-3eeb-46b7-99e8-f554b8f81994" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_5a4cb3e9-95e5-4a88-9bf4-cde4cf09f145" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_6f7d866e-3eeb-46b7-99e8-f554b8f81994" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_472870ef-a426-4d25-a647-6fb008758d5b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_6f7d866e-3eeb-46b7-99e8-f554b8f81994" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_472870ef-a426-4d25-a647-6fb008758d5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_472870ef-a426-4d25-a647-6fb008758d5b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_472870ef-a426-4d25-a647-6fb008758d5b" xlink:to="loc_us-gaap_SegmentDomain_472870ef-a426-4d25-a647-6fb008758d5b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_63471c23-f19b-4f74-a49e-6656a3d846c8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_472870ef-a426-4d25-a647-6fb008758d5b" xlink:to="loc_us-gaap_SegmentDomain_63471c23-f19b-4f74-a49e-6656a3d846c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_e9a0c4ac-58c0-4668-936c-2d0812b3bf36" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_63471c23-f19b-4f74-a49e-6656a3d846c8" xlink:to="loc_dco_ElectronicSystemsSegmentMember_e9a0c4ac-58c0-4668-936c-2d0812b3bf36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_2a8e54fc-8707-4842-aede-c7e24eca3e4f" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_63471c23-f19b-4f74-a49e-6656a3d846c8" xlink:to="loc_dco_StructuralSystemsSegmentMember_2a8e54fc-8707-4842-aede-c7e24eca3e4f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/LongTermDebtSummaryDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#LongTermDebtSummaryDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/LongTermDebtSummaryDetails" xlink:type="extended" id="i4041678dfb284c3bac91d20dc17b0a36_LongTermDebtSummaryDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_f0593c49-6216-4373-abd8-a3691b22fdc0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_f0593c49-6216-4373-abd8-a3691b22fdc0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_ae8ba674-2b8b-4365-afdd-c9031f95a1ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:to="loc_us-gaap_LongTermDebtCurrent_ae8ba674-2b8b-4365-afdd-c9031f95a1ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_c0a40b58-fc7d-426b-8636-996c89b10e89" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_c0a40b58-fc7d-426b-8636-996c89b10e89" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_6e81990a-227a-48b7-8daf-1762ea85c4f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_6e81990a-227a-48b7-8daf-1762ea85c4f4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_91c3eece-4e6d-4cdc-99e1-5bbc8f18e1b7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:to="loc_us-gaap_LongTermDebt_91c3eece-4e6d-4cdc-99e1-5bbc8f18e1b7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_31c15911-751c-4aa5-bc47-614e61138797" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_a3896ec4-3af4-4e7d-822c-da04f5f13fc7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:to="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_a3896ec4-3af4-4e7d-822c-da04f5f13fc7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_13ac345b-b59a-40f9-969e-7f5f3d28f225" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2890633d-322d-4482-97b6-0e32b5edcf89" xlink:to="loc_us-gaap_DebtInstrumentTable_13ac345b-b59a-40f9-969e-7f5f3d28f225" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_55eeed56-65d8-4998-881d-e9a4efca811a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_13ac345b-b59a-40f9-969e-7f5f3d28f225" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_55eeed56-65d8-4998-881d-e9a4efca811a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_55eeed56-65d8-4998-881d-e9a4efca811a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_55eeed56-65d8-4998-881d-e9a4efca811a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_55eeed56-65d8-4998-881d-e9a4efca811a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_4539fed9-7ff0-43ad-93c8-ff3bbe22628d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_55eeed56-65d8-4998-881d-e9a4efca811a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_4539fed9-7ff0-43ad-93c8-ff3bbe22628d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SeniorSecuredTermLoanMember_e254ac5f-3f3d-4ea2-a021-d7280ba0254b" xlink:href="dco-20221231.xsd#dco_SeniorSecuredTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_4539fed9-7ff0-43ad-93c8-ff3bbe22628d" xlink:to="loc_dco_SeniorSecuredTermLoanMember_e254ac5f-3f3d-4ea2-a021-d7280ba0254b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_1b8e401a-df68-49ec-bf8c-ec157f7440a6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_4539fed9-7ff0-43ad-93c8-ff3bbe22628d" xlink:to="loc_us-gaap_LineOfCreditMember_1b8e401a-df68-49ec-bf8c-ec157f7440a6" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/LongTermDebtNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#LongTermDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/LongTermDebtNarrativeDetails" xlink:type="extended" id="i224edd711d8848dd9d5e6e9a372d5fd2_LongTermDebtNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_6a5fee53-8d10-498c-8b66-123fef2d1ab0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_6a5fee53-8d10-498c-8b66-123fef2d1ab0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_24d31a20-f715-4721-a81d-ca91dbd7fbb3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_24d31a20-f715-4721-a81d-ca91dbd7fbb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_5e56b031-96e1-4f80-8052-40247b02e019" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_5e56b031-96e1-4f80-8052-40247b02e019" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentBasisSpreadonFixedRateBaseRate_64e7f66d-7d40-48b5-b46f-81ba69815e00" xlink:href="dco-20221231.xsd#dco_DebtInstrumentBasisSpreadonFixedRateBaseRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_dco_DebtInstrumentBasisSpreadonFixedRateBaseRate_64e7f66d-7d40-48b5-b46f-81ba69815e00" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPrepaymentAmountPercentageofPrincipalAmount_0b47d5aa-3302-4c3d-a64f-629b09268312" xlink:href="dco-20221231.xsd#dco_DebtInstrumentPrepaymentAmountPercentageofPrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_dco_DebtInstrumentPrepaymentAmountPercentageofPrincipalAmount_0b47d5aa-3302-4c3d-a64f-629b09268312" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfDebt_3a21c875-de02-4446-ae96-714b0d165241" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_RepaymentsOfDebt_3a21c875-de02-4446-ae96-714b0d165241" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_ecc4ac93-91a4-42bc-8830-e65aa941098a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_ecc4ac93-91a4-42bc-8830-e65aa941098a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_640cfddf-09a5-44ea-8351-d09094e84153" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_640cfddf-09a5-44ea-8351-d09094e84153" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisGreaterthan3.25_597ee46d-44cf-41db-a179-396ede981007" xlink:href="dco-20221231.xsd#dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisGreaterthan3.25"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisGreaterthan3.25_597ee46d-44cf-41db-a179-396ede981007" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessthanorEqualto3.25_0656aebe-c6e8-4156-aeec-f83daa9c02fe" xlink:href="dco-20221231.xsd#dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessthanorEqualto3.25"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessthanorEqualto3.25_0656aebe-c6e8-4156-aeec-f83daa9c02fe" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMinimum_a1a90bb6-f2b0-4e93-8fb9-16da7aa216ad" xlink:href="dco-20221231.xsd#dco_DebtInstrumentCovenantAdjustedLeverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMinimum_a1a90bb6-f2b0-4e93-8fb9-16da7aa216ad" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMaximum_d1083ec9-5859-42d8-ba4e-9401eeb31ad1" xlink:href="dco-20221231.xsd#dco_DebtInstrumentCovenantAdjustedLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMaximum_d1083ec9-5859-42d8-ba4e-9401eeb31ad1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessThanorEqualto2.50_8038ba92-fa3d-41e1-9b4c-0a23b45d9da4" xlink:href="dco-20221231.xsd#dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessThanorEqualto2.50"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessThanorEqualto2.50_8038ba92-fa3d-41e1-9b4c-0a23b45d9da4" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_aa028b69-a0e4-4aa2-a672-02b31a1f449f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_aa028b69-a0e4-4aa2-a672-02b31a1f449f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfSecuredDebt_5d7ba5b7-9d19-48bc-8c5c-bc5423806be3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfSecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_RepaymentsOfSecuredDebt_5d7ba5b7-9d19-48bc-8c5c-bc5423806be3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_81521cc9-78c0-48cb-aaac-dccf8b9cbced" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_81521cc9-78c0-48cb-aaac-dccf8b9cbced" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_16876899-3e74-426d-b60d-37b98efc8ae8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_16876899-3e74-426d-b60d-37b98efc8ae8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_b178af1b-9da4-410b-ada0-331bf1cbac9c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_b178af1b-9da4-410b-ada0-331bf1cbac9c" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_de81e25e-9a6c-46d2-a377-277f993f2f44" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_de81e25e-9a6c-46d2-a377-277f993f2f44" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_3663362f-8fd6-4b8b-a925-3ee943f22ccd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_3663362f-8fd6-4b8b-a925-3ee943f22ccd" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_874f5111-1a9e-4cac-bd0e-65a93f0441bb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_874f5111-1a9e-4cac-bd0e-65a93f0441bb" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_6ca97354-36a1-4982-9ec1-2be792f5b670" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_6ca97354-36a1-4982-9ec1-2be792f5b670" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_accedd44-c571-41f2-a9d9-36313626af6b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_accedd44-c571-41f2-a9d9-36313626af6b" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_66f7ccd1-2f19-4f4b-a4d0-49dd8a219a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_66f7ccd1-2f19-4f4b-a4d0-49dd8a219a7b" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLeasePaymentSalesTypeAndDirectFinancingLeasesInvestingActivity_da78af3b-3245-4c40-9b3a-ae174581af55" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromLeasePaymentSalesTypeAndDirectFinancingLeasesInvestingActivity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_ProceedsFromLeasePaymentSalesTypeAndDirectFinancingLeasesInvestingActivity_da78af3b-3245-4c40-9b3a-ae174581af55" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_407e4515-c071-4777-8d06-353c017a7989" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_DerivativeNotionalAmount_407e4515-c071-4777-8d06-353c017a7989" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAverageFixedInterestRate_262cb4dc-5365-4e3a-b7c5-324bb7bdfcc2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeAverageFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_DerivativeAverageFixedInterestRate_262cb4dc-5365-4e3a-b7c5-324bb7bdfcc2" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_c6c5d867-ddb3-4cc9-ad36-bededa655bd4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_c6c5d867-ddb3-4cc9-ad36-bededa655bd4" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingAssetsNoncurrent_b3dd88bd-3fe5-432b-ac33-23c396f5c9ab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_HedgingAssetsNoncurrent_b3dd88bd-3fe5-432b-ac33-23c396f5c9ab" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForHedgeFinancingActivities_73eaa757-9ac4-4e9a-a23a-4c1f099c70f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForHedgeFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_PaymentsForHedgeFinancingActivities_73eaa757-9ac4-4e9a-a23a-4c1f099c70f2" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de76d9d5-d67b-4f6f-bde1-38066cf9b4f8" xlink:to="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_f268da85-a2ce-4528-b567-ede604718324" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_us-gaap_CreditFacilityAxis_f268da85-a2ce-4528-b567-ede604718324" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f268da85-a2ce-4528-b567-ede604718324_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_f268da85-a2ce-4528-b567-ede604718324" xlink:to="loc_us-gaap_CreditFacilityDomain_f268da85-a2ce-4528-b567-ede604718324_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_0f34a0d1-6bf2-449e-905f-e2dcf1e715b8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_f268da85-a2ce-4528-b567-ede604718324" xlink:to="loc_us-gaap_CreditFacilityDomain_0f34a0d1-6bf2-449e-905f-e2dcf1e715b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_b7bed0c5-92e0-4231-b1de-b1ef943b0d22" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_0f34a0d1-6bf2-449e-905f-e2dcf1e715b8" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_b7bed0c5-92e0-4231-b1de-b1ef943b0d22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_75daf3cf-4ef6-4ec2-b477-f72ef71edd19" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_0f34a0d1-6bf2-449e-905f-e2dcf1e715b8" xlink:to="loc_us-gaap_SecuredDebtMember_75daf3cf-4ef6-4ec2-b477-f72ef71edd19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_41296c3e-aa7f-4744-8f5a-d721bc142cfb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_us-gaap_DebtInstrumentAxis_41296c3e-aa7f-4744-8f5a-d721bc142cfb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_41296c3e-aa7f-4744-8f5a-d721bc142cfb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_41296c3e-aa7f-4744-8f5a-d721bc142cfb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_41296c3e-aa7f-4744-8f5a-d721bc142cfb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_41296c3e-aa7f-4744-8f5a-d721bc142cfb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NewRevolvingCreditFacilityDueDecember202024Member_0737ca50-26ad-41a5-ae44-872580a644e8" xlink:href="dco-20221231.xsd#dco_NewRevolvingCreditFacilityDueDecember202024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_NewRevolvingCreditFacilityDueDecember202024Member_0737ca50-26ad-41a5-ae44-872580a644e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_New2018RevolvingCreditFacilityMaturingNovember212023Member_c19874a3-7cf3-47e3-b4ff-c6a757a88dbe" xlink:href="dco-20221231.xsd#dco_New2018RevolvingCreditFacilityMaturingNovember212023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_New2018RevolvingCreditFacilityMaturingNovember212023Member_c19874a3-7cf3-47e3-b4ff-c6a757a88dbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NewTermLoanMaturingDecember202024Member_11df24ee-4402-47ca-b92f-b1efc688d465" xlink:href="dco-20221231.xsd#dco_NewTermLoanMaturingDecember202024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_NewTermLoanMaturingDecember202024Member_11df24ee-4402-47ca-b92f-b1efc688d465" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_New2018TermLoanMaturingNovember212025Member_c526669e-75cb-4a40-9869-cb489f587ece" xlink:href="dco-20221231.xsd#dco_New2018TermLoanMaturingNovember212025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_New2018TermLoanMaturingNovember212025Member_c526669e-75cb-4a40-9869-cb489f587ece" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_CreditFacilitiesMember_f0d1ad68-4421-4789-83c9-3e037a685815" xlink:href="dco-20221231.xsd#dco_CreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_CreditFacilitiesMember_f0d1ad68-4421-4789-83c9-3e037a685815" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2022RevolvingCreditFacilitiesMember_470ee2a7-2855-4867-9912-4b09fa657298" xlink:href="dco-20221231.xsd#dco_A2022RevolvingCreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_A2022RevolvingCreditFacilitiesMember_470ee2a7-2855-4867-9912-4b09fa657298" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2022TermLoanMaturingJuly142027Member_ef2728d5-9bf3-42fc-87a2-7864e704166b" xlink:href="dco-20221231.xsd#dco_A2022TermLoanMaturingJuly142027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_A2022TermLoanMaturingJuly142027Member_ef2728d5-9bf3-42fc-87a2-7864e704166b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2022RevolvingCreditFacilityDueJuly142027Member_6e2653c3-82d1-482b-84e4-17d1483d7a70" xlink:href="dco-20221231.xsd#dco_A2022RevolvingCreditFacilityDueJuly142027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_A2022RevolvingCreditFacilityDueJuly142027Member_6e2653c3-82d1-482b-84e4-17d1483d7a70" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2019TermLoanMaturingDecember202024Member_57037211-51bb-4280-98b9-d248d973718e" xlink:href="dco-20221231.xsd#dco_A2019TermLoanMaturingDecember202024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_A2019TermLoanMaturingDecember202024Member_57037211-51bb-4280-98b9-d248d973718e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2019RevolvingCreditFacilityDueDecember202024Member_f1b00aae-7146-4264-8d89-5382cf4cdf76" xlink:href="dco-20221231.xsd#dco_A2019RevolvingCreditFacilityDueDecember202024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e6af2612-4699-4d51-97fb-6daad99766cf" xlink:to="loc_dco_A2019RevolvingCreditFacilityDueDecember202024Member_f1b00aae-7146-4264-8d89-5382cf4cdf76" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_0c1a9b9a-8a9c-413d-92d9-998e99ee3ed8" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_srt_RangeAxis_0c1a9b9a-8a9c-413d-92d9-998e99ee3ed8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0c1a9b9a-8a9c-413d-92d9-998e99ee3ed8_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_0c1a9b9a-8a9c-413d-92d9-998e99ee3ed8" xlink:to="loc_srt_RangeMember_0c1a9b9a-8a9c-413d-92d9-998e99ee3ed8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1e7fce2a-c27e-47ed-896d-7db215aa8dc9" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_0c1a9b9a-8a9c-413d-92d9-998e99ee3ed8" xlink:to="loc_srt_RangeMember_1e7fce2a-c27e-47ed-896d-7db215aa8dc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_980225a9-5eea-4e1e-9fd3-9f83d769d6d7" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1e7fce2a-c27e-47ed-896d-7db215aa8dc9" xlink:to="loc_srt_MinimumMember_980225a9-5eea-4e1e-9fd3-9f83d769d6d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fb60dd31-d762-428f-8eb3-e9db762344cf" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1e7fce2a-c27e-47ed-896d-7db215aa8dc9" xlink:to="loc_srt_MaximumMember_fb60dd31-d762-428f-8eb3-e9db762344cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_066b4a64-bfec-412b-90c6-dc108ea6529e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_us-gaap_VariableRateAxis_066b4a64-bfec-412b-90c6-dc108ea6529e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_066b4a64-bfec-412b-90c6-dc108ea6529e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_066b4a64-bfec-412b-90c6-dc108ea6529e" xlink:to="loc_us-gaap_VariableRateDomain_066b4a64-bfec-412b-90c6-dc108ea6529e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_83652e6c-57c8-435c-8e1e-37c5128075e9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_066b4a64-bfec-412b-90c6-dc108ea6529e" xlink:to="loc_us-gaap_VariableRateDomain_83652e6c-57c8-435c-8e1e-37c5128075e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_4fef3a33-e98b-4975-9fc3-6208ea139cae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_83652e6c-57c8-435c-8e1e-37c5128075e9" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_4fef3a33-e98b-4975-9fc3-6208ea139cae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_bebe7f38-d32a-4198-972e-2965c62a87f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_83652e6c-57c8-435c-8e1e-37c5128075e9" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_bebe7f38-d32a-4198-972e-2965c62a87f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EurodollarMember_a43352f7-5f54-46e7-bc43-231f9a0bb7e2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EurodollarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_83652e6c-57c8-435c-8e1e-37c5128075e9" xlink:to="loc_us-gaap_EurodollarMember_a43352f7-5f54-46e7-bc43-231f9a0bb7e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_b9742672-efce-4cf1-a6b1-c3ee45a896f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_83652e6c-57c8-435c-8e1e-37c5128075e9" xlink:to="loc_us-gaap_BaseRateMember_b9742672-efce-4cf1-a6b1-c3ee45a896f4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_a74b4edb-dfd5-457e-b7fe-4cc4e504cea6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_83652e6c-57c8-435c-8e1e-37c5128075e9" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_a74b4edb-dfd5-457e-b7fe-4cc4e504cea6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_da77e240-5019-4413-ba57-21ca6d1b2945" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_da77e240-5019-4413-ba57-21ca6d1b2945" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_da77e240-5019-4413-ba57-21ca6d1b2945_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_da77e240-5019-4413-ba57-21ca6d1b2945" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_da77e240-5019-4413-ba57-21ca6d1b2945_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_212c0ac2-f1bc-4600-ab09-a94e6be57071" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_da77e240-5019-4413-ba57-21ca6d1b2945" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_212c0ac2-f1bc-4600-ab09-a94e6be57071" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_ca216caf-8d15-4ac2-b1a5-131fc81ab709" xlink:href="dco-20221231.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_212c0ac2-f1bc-4600-ab09-a94e6be57071" xlink:to="loc_dco_MagneticSealCorporationMember_ca216caf-8d15-4ac2-b1a5-131fc81ab709" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_3c935034-b7af-4e74-8b45-9150c6aa9593" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_3c935034-b7af-4e74-8b45-9150c6aa9593" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_3c935034-b7af-4e74-8b45-9150c6aa9593_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3c935034-b7af-4e74-8b45-9150c6aa9593" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_3c935034-b7af-4e74-8b45-9150c6aa9593_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_7fb7e892-b400-47e1-be36-8f4affd3995d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3c935034-b7af-4e74-8b45-9150c6aa9593" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_7fb7e892-b400-47e1-be36-8f4affd3995d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_8e7661f5-0c9f-4e08-bd4e-0ca3a29bfff2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_7fb7e892-b400-47e1-be36-8f4affd3995d" xlink:to="loc_us-gaap_InterestRateSwapMember_8e7661f5-0c9f-4e08-bd4e-0ca3a29bfff2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCapMember_08238be7-a1e5-42bc-8250-f03933094c22" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestRateCapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_7fb7e892-b400-47e1-be36-8f4affd3995d" xlink:to="loc_us-gaap_InterestRateCapMember_08238be7-a1e5-42bc-8250-f03933094c22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentConvenantAxis_e8f87d34-170c-4486-ab5d-1cc0a1e28857" xlink:href="dco-20221231.xsd#dco_DebtInstrumentConvenantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_dco_DebtInstrumentConvenantAxis_e8f87d34-170c-4486-ab5d-1cc0a1e28857" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentConvenantDomain_e8f87d34-170c-4486-ab5d-1cc0a1e28857_default" xlink:href="dco-20221231.xsd#dco_DebtInstrumentConvenantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dco_DebtInstrumentConvenantAxis_e8f87d34-170c-4486-ab5d-1cc0a1e28857" xlink:to="loc_dco_DebtInstrumentConvenantDomain_e8f87d34-170c-4486-ab5d-1cc0a1e28857_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentConvenantDomain_44f10026-aba5-4a62-bf8f-e43c2888694d" xlink:href="dco-20221231.xsd#dco_DebtInstrumentConvenantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dco_DebtInstrumentConvenantAxis_e8f87d34-170c-4486-ab5d-1cc0a1e28857" xlink:to="loc_dco_DebtInstrumentConvenantDomain_44f10026-aba5-4a62-bf8f-e43c2888694d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenant50OfExcessCashFlowAmountMember_3301c299-e13d-4599-b1aa-cf3fe9c00ff1" xlink:href="dco-20221231.xsd#dco_DebtInstrumentCovenant50OfExcessCashFlowAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentConvenantDomain_44f10026-aba5-4a62-bf8f-e43c2888694d" xlink:to="loc_dco_DebtInstrumentCovenant50OfExcessCashFlowAmountMember_3301c299-e13d-4599-b1aa-cf3fe9c00ff1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenant25OfExcessCashFlowAmountMember_d149a757-caf0-4d0c-998f-b44118d6b39b" xlink:href="dco-20221231.xsd#dco_DebtInstrumentCovenant25OfExcessCashFlowAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentConvenantDomain_44f10026-aba5-4a62-bf8f-e43c2888694d" xlink:to="loc_dco_DebtInstrumentCovenant25OfExcessCashFlowAmountMember_d149a757-caf0-4d0c-998f-b44118d6b39b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenant0OfExcessCashFlowAmountMember_8dd8f2ed-6244-42bf-9417-c70556aec8d4" xlink:href="dco-20221231.xsd#dco_DebtInstrumentCovenant0OfExcessCashFlowAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentConvenantDomain_44f10026-aba5-4a62-bf8f-e43c2888694d" xlink:to="loc_dco_DebtInstrumentCovenant0OfExcessCashFlowAmountMember_8dd8f2ed-6244-42bf-9417-c70556aec8d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_86998cc9-f1c2-45de-aebe-1e7caa3c3c3a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_us-gaap_HedgingDesignationAxis_86998cc9-f1c2-45de-aebe-1e7caa3c3c3a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_86998cc9-f1c2-45de-aebe-1e7caa3c3c3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_86998cc9-f1c2-45de-aebe-1e7caa3c3c3a" xlink:to="loc_us-gaap_HedgingDesignationDomain_86998cc9-f1c2-45de-aebe-1e7caa3c3c3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_16e0e305-6857-4256-bbed-e2babb78ad48" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_86998cc9-f1c2-45de-aebe-1e7caa3c3c3a" xlink:to="loc_us-gaap_HedgingDesignationDomain_16e0e305-6857-4256-bbed-e2babb78ad48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_f2cfd385-0d89-4f8e-a918-fb6f75cf3cf6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_16e0e305-6857-4256-bbed-e2babb78ad48" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_f2cfd385-0d89-4f8e-a918-fb6f75cf3cf6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_b6756ed5-c593-4242-83d4-111931c9f910" xlink:href="dco-20221231.xsd#dco_DebtInstrumentQuarterlyPrepaymentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_309a6899-69d7-4d3c-80ab-98b5c20d6842" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_b6756ed5-c593-4242-83d4-111931c9f910" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_b6756ed5-c593-4242-83d4-111931c9f910_default" xlink:href="dco-20221231.xsd#dco_DebtInstrumentQuarterlyPrepaymentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_b6756ed5-c593-4242-83d4-111931c9f910" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_b6756ed5-c593-4242-83d4-111931c9f910_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_34cdd871-132c-4605-8685-cfaa74796066" xlink:href="dco-20221231.xsd#dco_DebtInstrumentQuarterlyPrepaymentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_b6756ed5-c593-4242-83d4-111931c9f910" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_34cdd871-132c-4605-8685-cfaa74796066" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentYearOneAndYearTwoMember_7d178993-5284-4592-adfd-ffd72b4e8e7c" xlink:href="dco-20221231.xsd#dco_DebtInstrumentQuarterlyPrepaymentYearOneAndYearTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_34cdd871-132c-4605-8685-cfaa74796066" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentYearOneAndYearTwoMember_7d178993-5284-4592-adfd-ffd72b4e8e7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentYearThreeAndYearFourMember_c6f47684-63fa-403b-aa00-01a64fb35d03" xlink:href="dco-20221231.xsd#dco_DebtInstrumentQuarterlyPrepaymentYearThreeAndYearFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_34cdd871-132c-4605-8685-cfaa74796066" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentYearThreeAndYearFourMember_c6f47684-63fa-403b-aa00-01a64fb35d03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentYearFiveMember_a3215e92-92de-4c7f-b39d-52854b9e6b5e" xlink:href="dco-20221231.xsd#dco_DebtInstrumentQuarterlyPrepaymentYearFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_34cdd871-132c-4605-8685-cfaa74796066" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentYearFiveMember_a3215e92-92de-4c7f-b39d-52854b9e6b5e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended" id="i4514e992cc1b48cd81ba257a99c18b5b_StockBasedCompensationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofIncentivePlans_39a028c8-f780-4c14-a555-5542dc41b5b5" xlink:href="dco-20221231.xsd#dco_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofIncentivePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_dco_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofIncentivePlans_39a028c8-f780-4c14-a555-5542dc41b5b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c53589b3-be82-4d9f-931d-4746134937a2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c53589b3-be82-4d9f-931d-4746134937a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_8b0053aa-d590-472c-82d7-3f5d0237ba85" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_8b0053aa-d590-472c-82d7-3f5d0237ba85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate_77358902-5908-48ef-bb66-a2036a69d3f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate_77358902-5908-48ef-bb66-a2036a69d3f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod_60ff8ca7-9843-4b10-b783-9c7cc73410a9" xlink:href="dco-20221231.xsd#dco_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_dco_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriod_60ff8ca7-9843-4b10-b783-9c7cc73410a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SharebasedCompensationArrangementbySharebasedPaymentAwardMaximumPercentageofEmployeeCompensationforPurchaseofCommonStock_541ee37e-5d98-4781-8ffb-791003d338ca" xlink:href="dco-20221231.xsd#dco_SharebasedCompensationArrangementbySharebasedPaymentAwardMaximumPercentageofEmployeeCompensationforPurchaseofCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_dco_SharebasedCompensationArrangementbySharebasedPaymentAwardMaximumPercentageofEmployeeCompensationforPurchaseofCommonStock_541ee37e-5d98-4781-8ffb-791003d338ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_5fd33205-0e36-482a-b5ea-1b009208e4ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_5fd33205-0e36-482a-b5ea-1b009208e4ef" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0282fbca-dcc0-44f0-a3c2-e7e12611581a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0282fbca-dcc0-44f0-a3c2-e7e12611581a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_b18b4624-2288-42ec-af3e-f7e0dce2c63c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_b18b4624-2288-42ec-af3e-f7e0dce2c63c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_4baf8636-ddb4-4227-af33-b9dc51480262" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_4baf8636-ddb4-4227-af33-b9dc51480262" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_2f0055da-8363-458f-a2b5-fab3d5bd0a11" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_2f0055da-8363-458f-a2b5-fab3d5bd0a11" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProceedsFromExerciseOfStockOptionsAndOtherStockIssuances_48336bea-7f85-419d-9b3f-afaad3f4200b" xlink:href="dco-20221231.xsd#dco_ProceedsFromExerciseOfStockOptionsAndOtherStockIssuances"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_dco_ProceedsFromExerciseOfStockOptionsAndOtherStockIssuances_48336bea-7f85-419d-9b3f-afaad3f4200b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_TaxBenefitForExerciseOfStockOptionsAndIssuanceOfSharesUponVestingOfRestrictedStockGrants_963a031a-6e2b-4729-bac5-4700429eef65" xlink:href="dco-20221231.xsd#dco_TaxBenefitForExerciseOfStockOptionsAndIssuanceOfSharesUponVestingOfRestrictedStockGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_dco_TaxBenefitForExerciseOfStockOptionsAndIssuanceOfSharesUponVestingOfRestrictedStockGrants_963a031a-6e2b-4729-bac5-4700429eef65" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_b7296639-563a-4f20-a807-e6bd2fa232cf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_b7296639-563a-4f20-a807-e6bd2fa232cf" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_de7eda91-6755-4e19-89b4-7f77aceb7f55" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_de7eda91-6755-4e19-89b4-7f77aceb7f55" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_6fcafb06-8644-4d5e-9d95-1f3037328f95" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_6fcafb06-8644-4d5e-9d95-1f3037328f95" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_8e23f055-8a2c-449b-964c-3696e357e4c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_8e23f055-8a2c-449b-964c-3696e357e4c3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_c156e356-8b08-49db-bba1-bdeafd3660db" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_c156e356-8b08-49db-bba1-bdeafd3660db" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_10df7b56-4251-482f-bde3-b293c1db84e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_10df7b56-4251-482f-bde3-b293c1db84e4" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1d95f263-cb51-4b5d-b7d4-c2518a63bafd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1d95f263-cb51-4b5d-b7d4-c2518a63bafd" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_26089e11-af6d-4ef6-9241-00f86e21b968" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_26089e11-af6d-4ef6-9241-00f86e21b968" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_52cb87e3-2ad2-46ee-aea1-0cc4b50a4976" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_52cb87e3-2ad2-46ee-aea1-0cc4b50a4976" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_625a2c0e-79cb-48f8-80f6-42a068f5cde7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_625a2c0e-79cb-48f8-80f6-42a068f5cde7" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_415141dc-533e-4693-90e7-72b38971331f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_415141dc-533e-4693-90e7-72b38971331f" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_83ffa676-7f67-42b5-9528-68a86ee4efe9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_83ffa676-7f67-42b5-9528-68a86ee4efe9" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_e347694a-11fd-459c-8ebd-1a85ae3b2c4f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_e347694a-11fd-459c-8ebd-1a85ae3b2c4f" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_5a9a073c-751e-4b39-b0f3-31a850d3ff49" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_5a9a073c-751e-4b39-b0f3-31a850d3ff49" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_263e771e-2768-45e4-b903-68603e8b42aa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07a9b0a8-aaed-424f-95ee-31a1f77c9342" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_263e771e-2768-45e4-b903-68603e8b42aa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_f3b71d10-d64e-45b1-8001-5e5f0d857a9c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_263e771e-2768-45e4-b903-68603e8b42aa" xlink:to="loc_us-gaap_PlanNameAxis_f3b71d10-d64e-45b1-8001-5e5f0d857a9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_f3b71d10-d64e-45b1-8001-5e5f0d857a9c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_f3b71d10-d64e-45b1-8001-5e5f0d857a9c" xlink:to="loc_us-gaap_PlanNameDomain_f3b71d10-d64e-45b1-8001-5e5f0d857a9c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_c3e11c64-ca3e-43f9-b3bb-731f5b4c35f5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_f3b71d10-d64e-45b1-8001-5e5f0d857a9c" xlink:to="loc_us-gaap_PlanNameDomain_c3e11c64-ca3e-43f9-b3bb-731f5b4c35f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2020StockIncentivePlanThe2020PlanMember_ebc532f5-a6d9-40fa-9ea8-7c8654a0f1e2" xlink:href="dco-20221231.xsd#dco_A2020StockIncentivePlanThe2020PlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_c3e11c64-ca3e-43f9-b3bb-731f5b4c35f5" xlink:to="loc_dco_A2020StockIncentivePlanThe2020PlanMember_ebc532f5-a6d9-40fa-9ea8-7c8654a0f1e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f3596ab8-6083-40f9-ad62-0884079c3b51" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_263e771e-2768-45e4-b903-68603e8b42aa" xlink:to="loc_us-gaap_AwardTypeAxis_f3596ab8-6083-40f9-ad62-0884079c3b51" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f3596ab8-6083-40f9-ad62-0884079c3b51_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f3596ab8-6083-40f9-ad62-0884079c3b51" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f3596ab8-6083-40f9-ad62-0884079c3b51_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f71f821b-7bda-438e-9d7f-145a488a1796" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f3596ab8-6083-40f9-ad62-0884079c3b51" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f71f821b-7bda-438e-9d7f-145a488a1796" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_691ef578-a597-4bad-8bab-16e46eff3620" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f71f821b-7bda-438e-9d7f-145a488a1796" xlink:to="loc_us-gaap_EmployeeStockMember_691ef578-a597-4bad-8bab-16e46eff3620" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_4961e2ab-9f53-4ca7-a71a-80e91b276e3d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f71f821b-7bda-438e-9d7f-145a488a1796" xlink:to="loc_us-gaap_EmployeeStockOptionMember_4961e2ab-9f53-4ca7-a71a-80e91b276e3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_35015be8-72d7-4318-9438-0ee56e46314e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f71f821b-7bda-438e-9d7f-145a488a1796" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_35015be8-72d7-4318-9438-0ee56e46314e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_9e5279c7-abeb-4885-a44e-c1e3a591735a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f71f821b-7bda-438e-9d7f-145a488a1796" xlink:to="loc_us-gaap_PerformanceSharesMember_9e5279c7-abeb-4885-a44e-c1e3a591735a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PerformanceBasedWithMarketConditionCashSettledLongTermIncentiveAwardsMember_1e67c755-74eb-4c2d-bf9f-ba9f8d020d25" xlink:href="dco-20221231.xsd#dco_PerformanceBasedWithMarketConditionCashSettledLongTermIncentiveAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f71f821b-7bda-438e-9d7f-145a488a1796" xlink:to="loc_dco_PerformanceBasedWithMarketConditionCashSettledLongTermIncentiveAwardsMember_1e67c755-74eb-4c2d-bf9f-ba9f8d020d25" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_401e860a-63af-4429-a5c0-31488aebb1b5" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_263e771e-2768-45e4-b903-68603e8b42aa" xlink:to="loc_srt_RangeAxis_401e860a-63af-4429-a5c0-31488aebb1b5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_401e860a-63af-4429-a5c0-31488aebb1b5_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_401e860a-63af-4429-a5c0-31488aebb1b5" xlink:to="loc_srt_RangeMember_401e860a-63af-4429-a5c0-31488aebb1b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8b398cf0-9118-443a-8315-097c514bed10" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_401e860a-63af-4429-a5c0-31488aebb1b5" xlink:to="loc_srt_RangeMember_8b398cf0-9118-443a-8315-097c514bed10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_a40114a1-e4d7-486d-94b9-05429fc29ab7" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8b398cf0-9118-443a-8315-097c514bed10" xlink:to="loc_srt_MinimumMember_a40114a1-e4d7-486d-94b9-05429fc29ab7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a1ef7648-cacd-43e0-98e0-a66e6984d89c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_8b398cf0-9118-443a-8315-097c514bed10" xlink:to="loc_srt_MaximumMember_a1ef7648-cacd-43e0-98e0-a66e6984d89c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_539c08c3-abac-45c4-b7b5-a4aca7bcfc16" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_263e771e-2768-45e4-b903-68603e8b42aa" xlink:to="loc_us-gaap_VestingAxis_539c08c3-abac-45c4-b7b5-a4aca7bcfc16" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_539c08c3-abac-45c4-b7b5-a4aca7bcfc16_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_539c08c3-abac-45c4-b7b5-a4aca7bcfc16" xlink:to="loc_us-gaap_VestingDomain_539c08c3-abac-45c4-b7b5-a4aca7bcfc16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_b79cc2e0-27ee-4b84-8e77-603c7539cd22" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_539c08c3-abac-45c4-b7b5-a4aca7bcfc16" xlink:to="loc_us-gaap_VestingDomain_b79cc2e0-27ee-4b84-8e77-603c7539cd22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_75ddf06c-2e1a-4601-83e4-97d5c340da6a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_b79cc2e0-27ee-4b84-8e77-603c7539cd22" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_75ddf06c-2e1a-4601-83e4-97d5c340da6a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_5411ed02-7e2e-45dd-a019-868f5ebe9345" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_b79cc2e0-27ee-4b84-8e77-603c7539cd22" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_5411ed02-7e2e-45dd-a019-868f5ebe9345" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_7f741c05-7d26-4912-90b2-849bff52d31c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_b79cc2e0-27ee-4b84-8e77-603c7539cd22" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_7f741c05-7d26-4912-90b2-849bff52d31c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/StockBasedCompensationAssumptionsUsedforEstimatingFairValueofShareBasedPaymentAwardDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#StockBasedCompensationAssumptionsUsedforEstimatingFairValueofShareBasedPaymentAwardDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/StockBasedCompensationAssumptionsUsedforEstimatingFairValueofShareBasedPaymentAwardDetails" xlink:type="extended" id="ic2baee54a074491fa85eb4d0140f5ef6_StockBasedCompensationAssumptionsUsedforEstimatingFairValueofShareBasedPaymentAwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0fea06a-077c-4357-a2fc-df7571162fc5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_609a16ae-d8ff-4dc1-972d-15bd021c86cf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0fea06a-077c-4357-a2fc-df7571162fc5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_609a16ae-d8ff-4dc1-972d-15bd021c86cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_5458d997-3f6d-4849-b430-c21e8be0f08a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0fea06a-077c-4357-a2fc-df7571162fc5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_5458d997-3f6d-4849-b430-c21e8be0f08a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments_879af5a3-1785-4fb7-8b4e-a8b7b3b56d38" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0fea06a-077c-4357-a2fc-df7571162fc5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendPayments_879af5a3-1785-4fb7-8b4e-a8b7b3b56d38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_1861678b-af3e-410e-95d6-564657bc360b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0fea06a-077c-4357-a2fc-df7571162fc5" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_1861678b-af3e-410e-95d6-564657bc360b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_bde6f444-dc1c-42b6-983f-490e0f8966bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0fea06a-077c-4357-a2fc-df7571162fc5" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_bde6f444-dc1c-42b6-983f-490e0f8966bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f92e35fc-4642-4ba7-ac39-8b5a3b29a010" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_bde6f444-dc1c-42b6-983f-490e0f8966bf" xlink:to="loc_us-gaap_AwardTypeAxis_f92e35fc-4642-4ba7-ac39-8b5a3b29a010" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f92e35fc-4642-4ba7-ac39-8b5a3b29a010_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f92e35fc-4642-4ba7-ac39-8b5a3b29a010" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f92e35fc-4642-4ba7-ac39-8b5a3b29a010_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c0688f5b-bcff-4643-a9bb-b70ed5430bba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f92e35fc-4642-4ba7-ac39-8b5a3b29a010" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c0688f5b-bcff-4643-a9bb-b70ed5430bba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_f2759980-1817-4a95-8371-d056c2e90737" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c0688f5b-bcff-4643-a9bb-b70ed5430bba" xlink:to="loc_us-gaap_EmployeeStockOptionMember_f2759980-1817-4a95-8371-d056c2e90737" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/StockBasedCompensationRestrictedStockActivityDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#StockBasedCompensationRestrictedStockActivityDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/StockBasedCompensationRestrictedStockActivityDetails" xlink:type="extended" id="i762aa813003a49aea16ee1fc7c62b2a6_StockBasedCompensationRestrictedStockActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b5b3cd40-c51d-4cfa-b94a-ab63203b450e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e2209153-081b-4547-9d43-9c622ec5f851" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b5b3cd40-c51d-4cfa-b94a-ab63203b450e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e2209153-081b-4547-9d43-9c622ec5f851" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_183b44d8-bd8f-48d4-953d-1d641d226e99" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e2209153-081b-4547-9d43-9c622ec5f851" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_183b44d8-bd8f-48d4-953d-1d641d226e99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_48c7c109-1677-4b13-b138-6bba1b8d9d40" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e2209153-081b-4547-9d43-9c622ec5f851" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_48c7c109-1677-4b13-b138-6bba1b8d9d40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_1c192a19-e9ba-43fa-8609-286982cae586" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e2209153-081b-4547-9d43-9c622ec5f851" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_1c192a19-e9ba-43fa-8609-286982cae586" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_dfce0903-2c32-42ca-a94a-4ccf4fcdd01a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_e2209153-081b-4547-9d43-9c622ec5f851" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_dfce0903-2c32-42ca-a94a-4ccf4fcdd01a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_618af2f2-d00e-4f64-968f-bb936e66f747" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_6ad2dd3f-792f-483b-b248-047b3ce1237d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b5b3cd40-c51d-4cfa-b94a-ab63203b450e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_6ad2dd3f-792f-483b-b248-047b3ce1237d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_541e98f9-8377-4be2-aa04-305ec89c8a0a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_6ad2dd3f-792f-483b-b248-047b3ce1237d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_541e98f9-8377-4be2-aa04-305ec89c8a0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_6d0f9bf4-0328-4fea-a6d0-66a8b48d63de" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_6ad2dd3f-792f-483b-b248-047b3ce1237d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_6d0f9bf4-0328-4fea-a6d0-66a8b48d63de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_5919ff20-a340-45f6-8852-d71bddf5893b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_6ad2dd3f-792f-483b-b248-047b3ce1237d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_5919ff20-a340-45f6-8852-d71bddf5893b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_54a3d38a-9ca5-4f7d-ac28-b343117e5048" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_6ad2dd3f-792f-483b-b248-047b3ce1237d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_54a3d38a-9ca5-4f7d-ac28-b343117e5048" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_90ac5bd3-f284-45fc-a065-65204b610444" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c4500a8a-9849-4722-aa0b-f144e4902e45" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b5b3cd40-c51d-4cfa-b94a-ab63203b450e" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c4500a8a-9849-4722-aa0b-f144e4902e45" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d8f801dd-a846-4213-9668-76b2dc665383" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c4500a8a-9849-4722-aa0b-f144e4902e45" xlink:to="loc_us-gaap_AwardTypeAxis_d8f801dd-a846-4213-9668-76b2dc665383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d8f801dd-a846-4213-9668-76b2dc665383_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d8f801dd-a846-4213-9668-76b2dc665383" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d8f801dd-a846-4213-9668-76b2dc665383_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_98d1d9fb-7045-44bf-9bbd-a892aed8c3e6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d8f801dd-a846-4213-9668-76b2dc665383" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_98d1d9fb-7045-44bf-9bbd-a892aed8c3e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_ff029de2-1d27-455a-ba3d-8e5d06986bbd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_98d1d9fb-7045-44bf-9bbd-a892aed8c3e6" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_ff029de2-1d27-455a-ba3d-8e5d06986bbd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_b0fae3c3-f337-4bd8-8a08-cbfbf67f2092" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_98d1d9fb-7045-44bf-9bbd-a892aed8c3e6" xlink:to="loc_us-gaap_PerformanceSharesMember_b0fae3c3-f337-4bd8-8a08-cbfbf67f2092" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/EmployeeBenefitPlansNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#EmployeeBenefitPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/EmployeeBenefitPlansNarrativeDetails" xlink:type="extended" id="i75c6db47221c4639a19107ab7e3c22c8_EmployeeBenefitPlansNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NumberOfDefinedContributionPlans_c25127e3-b00a-4a55-bf9c-88a4bdf3c7a8" xlink:href="dco-20221231.xsd#dco_NumberOfDefinedContributionPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_NumberOfDefinedContributionPlans_c25127e3-b00a-4a55-bf9c-88a4bdf3c7a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_13cfb0ba-681e-40b3-afa6-ce4932618b60" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_13cfb0ba-681e-40b3-afa6-ce4932618b60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedContributionPlanEmployerMatchingPercentOfEmployeeContribution_f871f246-0ffc-43b7-b2af-6dee66e47414" xlink:href="dco-20221231.xsd#dco_DefinedContributionPlanEmployerMatchingPercentOfEmployeeContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_DefinedContributionPlanEmployerMatchingPercentOfEmployeeContribution_f871f246-0ffc-43b7-b2af-6dee66e47414" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedContributionPlanEmployeeContributionsPercentageOfEligibleCompensation_2188fdc0-3058-4294-8a0a-f2734c6f9bfd" xlink:href="dco-20221231.xsd#dco_DefinedContributionPlanEmployeeContributionsPercentageOfEligibleCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_DefinedContributionPlanEmployeeContributionsPercentageOfEligibleCompensation_2188fdc0-3058-4294-8a0a-f2734c6f9bfd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedContributionPlanProvisionforMatchingandProfitSharingContributions_c26cd896-209f-433a-a0ef-7ad3cc977df3" xlink:href="dco-20221231.xsd#dco_DefinedContributionPlanProvisionforMatchingandProfitSharingContributions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_DefinedContributionPlanProvisionforMatchingandProfitSharingContributions_c26cd896-209f-433a-a0ef-7ad3cc977df3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedAmortizationNextFiscalYear_6a1e6681-6bcf-4886-8baf-2c231bb11113" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedAmortizationNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedAmortizationNextFiscalYear_6a1e6681-6bcf-4886-8baf-2c231bb11113" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedBenefitPlanPlanswithBenefitObligationsinExcessofPlanAssetsAmountinExcess_48da1f20-3080-41de-9ad4-fc367e04adb4" xlink:href="dco-20221231.xsd#dco_DefinedBenefitPlanPlanswithBenefitObligationsinExcessofPlanAssetsAmountinExcess"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_DefinedBenefitPlanPlanswithBenefitObligationsinExcessofPlanAssetsAmountinExcess_48da1f20-3080-41de-9ad4-fc367e04adb4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPensionPlanLiabilitiesNoncurrent_d12baec3-d41d-4913-b120-3bbce4633604" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPensionPlanLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_us-gaap_DefinedBenefitPensionPlanLiabilitiesNoncurrent_d12baec3-d41d-4913-b120-3bbce4633604" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedBenefitPlanNumberOfActivePlans_7c2c70e4-7484-4e2a-93f2-b08d8f6cd645" xlink:href="dco-20221231.xsd#dco_DefinedBenefitPlanNumberOfActivePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_DefinedBenefitPlanNumberOfActivePlans_7c2c70e4-7484-4e2a-93f2-b08d8f6cd645" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_7a29c0ca-a6a4-489b-a3c4-94cbd94a4fae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_7a29c0ca-a6a4-489b-a3c4-94cbd94a4fae" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NumberOfUnfundedSupplementalRetirementPlans_94b514fc-a566-4f8b-b214-e30f0cfd64b4" xlink:href="dco-20221231.xsd#dco_NumberOfUnfundedSupplementalRetirementPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_NumberOfUnfundedSupplementalRetirementPlans_94b514fc-a566-4f8b-b214-e30f0cfd64b4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PensionAndOtherPostretirementDefinedBenefitPlansAccruedEmployeesCompensationAndWithholdingsCurrentAndNoncurrent_dd190d95-1335-4c8e-9052-c7c6d5ec0159" xlink:href="dco-20221231.xsd#dco_PensionAndOtherPostretirementDefinedBenefitPlansAccruedEmployeesCompensationAndWithholdingsCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_PensionAndOtherPostretirementDefinedBenefitPlansAccruedEmployeesCompensationAndWithholdingsCurrentAndNoncurrent_dd190d95-1335-4c8e-9052-c7c6d5ec0159" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PensionObligationsAndOtherLongTermLiabilities_9e8dcf02-c35b-4a77-bee5-43ad4f8e627e" xlink:href="dco-20221231.xsd#dco_PensionObligationsAndOtherLongTermLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_PensionObligationsAndOtherLongTermLiabilities_9e8dcf02-c35b-4a77-bee5-43ad4f8e627e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_AccruedBenefitLiability_71d272c3-81f5-40eb-a684-4317fd57d8f6" xlink:href="dco-20221231.xsd#dco_AccruedBenefitLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_dco_AccruedBenefitLiability_71d272c3-81f5-40eb-a684-4317fd57d8f6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_76785ccc-7755-4afd-b7f4-467107fce477" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_a12c3a35-a57b-45cc-a343-0a9d7ea3c448" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_76785ccc-7755-4afd-b7f4-467107fce477" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e792b244-cb54-4296-b533-083929cddf44" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_76785ccc-7755-4afd-b7f4-467107fce477" xlink:to="loc_us-gaap_AwardTypeAxis_e792b244-cb54-4296-b533-083929cddf44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e792b244-cb54-4296-b533-083929cddf44_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e792b244-cb54-4296-b533-083929cddf44" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e792b244-cb54-4296-b533-083929cddf44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_464f32b6-0b59-4f87-8da5-319080ff7bb2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e792b244-cb54-4296-b533-083929cddf44" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_464f32b6-0b59-4f87-8da5-319080ff7bb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DeferredCompensationPlanMember_bbcaf60d-b643-47f8-8e4c-36837863d5cf" xlink:href="dco-20221231.xsd#dco_DeferredCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_464f32b6-0b59-4f87-8da5-319080ff7bb2" xlink:to="loc_dco_DeferredCompensationPlanMember_bbcaf60d-b643-47f8-8e4c-36837863d5cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_5cf169ef-a18b-45ef-bb3b-eb2f0a89c6fb" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_76785ccc-7755-4afd-b7f4-467107fce477" xlink:to="loc_srt_TitleOfIndividualAxis_5cf169ef-a18b-45ef-bb3b-eb2f0a89c6fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_5cf169ef-a18b-45ef-bb3b-eb2f0a89c6fb_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_5cf169ef-a18b-45ef-bb3b-eb2f0a89c6fb" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_5cf169ef-a18b-45ef-bb3b-eb2f0a89c6fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_8d625709-0ba7-483f-ad3a-75787c107f74" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_5cf169ef-a18b-45ef-bb3b-eb2f0a89c6fb" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_8d625709-0ba7-483f-ad3a-75787c107f74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ExecutivesandDirectorsMember_928d7efd-2ff1-4d71-b740-cc915bad7672" xlink:href="dco-20221231.xsd#dco_ExecutivesandDirectorsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_8d625709-0ba7-483f-ad3a-75787c107f74" xlink:to="loc_dco_ExecutivesandDirectorsMember_928d7efd-2ff1-4d71-b740-cc915bad7672" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanNameAxis_721ea85c-edea-49e7-831d-25c6d8a712f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_76785ccc-7755-4afd-b7f4-467107fce477" xlink:to="loc_us-gaap_RetirementPlanNameAxis_721ea85c-edea-49e7-831d-25c6d8a712f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanNameDomain_721ea85c-edea-49e7-831d-25c6d8a712f8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanNameAxis_721ea85c-edea-49e7-831d-25c6d8a712f8" xlink:to="loc_us-gaap_RetirementPlanNameDomain_721ea85c-edea-49e7-831d-25c6d8a712f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanNameDomain_7c10fed8-7b08-4798-8da3-4f2f249a4022" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanNameAxis_721ea85c-edea-49e7-831d-25c6d8a712f8" xlink:to="loc_us-gaap_RetirementPlanNameDomain_7c10fed8-7b08-4798-8da3-4f2f249a4022" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedContributionPlansParticipantGroupOneMember_f208a7c2-5151-4f5d-bf91-dec659b6906b" xlink:href="dco-20221231.xsd#dco_DefinedContributionPlansParticipantGroupOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanNameDomain_7c10fed8-7b08-4798-8da3-4f2f249a4022" xlink:to="loc_dco_DefinedContributionPlansParticipantGroupOneMember_f208a7c2-5151-4f5d-bf91-dec659b6906b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/EmployeeBenefitPlansPensionPlanAssetAllocationsDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#EmployeeBenefitPlansPensionPlanAssetAllocationsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/EmployeeBenefitPlansPensionPlanAssetAllocationsDetails" xlink:type="extended" id="i79644620434f435ab59d98322f12d8ac_EmployeeBenefitPlansPensionPlanAssetAllocationsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b924dc2d-64ce-4f58-aef5-9209110651c1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_265510c6-5919-4b01-9fd4-e8e8bb06f568" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b924dc2d-64ce-4f58-aef5-9209110651c1" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_265510c6-5919-4b01-9fd4-e8e8bb06f568" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_a0f7bbce-43ce-4c92-8459-0e6e0af5fb7d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_b924dc2d-64ce-4f58-aef5-9209110651c1" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_a0f7bbce-43ce-4c92-8459-0e6e0af5fb7d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_e404e548-50ad-43cc-ac12-126d484aebf9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_a0f7bbce-43ce-4c92-8459-0e6e0af5fb7d" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_e404e548-50ad-43cc-ac12-126d484aebf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_e404e548-50ad-43cc-ac12-126d484aebf9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_e404e548-50ad-43cc-ac12-126d484aebf9" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_e404e548-50ad-43cc-ac12-126d484aebf9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_30f534a9-85d4-4ee4-8057-5730da825f66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_e404e548-50ad-43cc-ac12-126d484aebf9" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_30f534a9-85d4-4ee4-8057-5730da825f66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_8bb69109-ab45-47ee-983e-95d1d14c2810" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanEquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_30f534a9-85d4-4ee4-8057-5730da825f66" xlink:to="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_8bb69109-ab45-47ee-983e-95d1d14c2810" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_c8f232c0-f014-4abe-8e1c-5840daea4af4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_30f534a9-85d4-4ee4-8057-5730da825f66" xlink:to="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_c8f232c0-f014-4abe-8e1c-5840daea4af4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_eeee28db-acde-4e14-a9b2-93d2058761d7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanDebtSecurityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_30f534a9-85d4-4ee4-8057-5730da825f66" xlink:to="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_eeee28db-acde-4e14-a9b2-93d2058761d7" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/EmployeeBenefitPlansAssetAllocationRangesDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#EmployeeBenefitPlansAssetAllocationRangesDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/EmployeeBenefitPlansAssetAllocationRangesDetails" xlink:type="extended" id="id7ed9038406e49ea9aedf0d6100a89e9_EmployeeBenefitPlansAssetAllocationRangesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_4efa633a-6bef-4ba2-9cd2-7eac7a22dc1b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage_765ba266-0311-4939-ad16-fb8ec4775c73" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_4efa633a-6bef-4ba2-9cd2-7eac7a22dc1b" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage_765ba266-0311-4939-ad16-fb8ec4775c73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_19859790-a7f3-4358-83e8-a74da4fe1e4d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_4efa633a-6bef-4ba2-9cd2-7eac7a22dc1b" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_19859790-a7f3-4358-83e8-a74da4fe1e4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_2754f787-6f6b-42ed-a446-cee561268f2b" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_19859790-a7f3-4358-83e8-a74da4fe1e4d" xlink:to="loc_srt_RangeAxis_2754f787-6f6b-42ed-a446-cee561268f2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2754f787-6f6b-42ed-a446-cee561268f2b_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_2754f787-6f6b-42ed-a446-cee561268f2b" xlink:to="loc_srt_RangeMember_2754f787-6f6b-42ed-a446-cee561268f2b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_605e4b66-0dfa-4919-bc07-31b8cbe4cb36" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_2754f787-6f6b-42ed-a446-cee561268f2b" xlink:to="loc_srt_RangeMember_605e4b66-0dfa-4919-bc07-31b8cbe4cb36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_a9b42fce-94de-4bc2-828e-bcf6d052d577" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_605e4b66-0dfa-4919-bc07-31b8cbe4cb36" xlink:to="loc_srt_MinimumMember_a9b42fce-94de-4bc2-828e-bcf6d052d577" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_0700747e-7e6c-4828-813d-ab21837baac7" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_605e4b66-0dfa-4919-bc07-31b8cbe4cb36" xlink:to="loc_srt_MaximumMember_0700747e-7e6c-4828-813d-ab21837baac7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8c484862-fd7a-46e0-8a23-849c5e1a51c4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_19859790-a7f3-4358-83e8-a74da4fe1e4d" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8c484862-fd7a-46e0-8a23-849c5e1a51c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_8c484862-fd7a-46e0-8a23-849c5e1a51c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8c484862-fd7a-46e0-8a23-849c5e1a51c4" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_8c484862-fd7a-46e0-8a23-849c5e1a51c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_6e7c3e46-7bb5-4e5b-9da2-b28183dd2390" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8c484862-fd7a-46e0-8a23-849c5e1a51c4" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_6e7c3e46-7bb5-4e5b-9da2-b28183dd2390" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashMember_f5ad43fd-398b-4602-a424-76bae813be6b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanCashMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_6e7c3e46-7bb5-4e5b-9da2-b28183dd2390" xlink:to="loc_us-gaap_DefinedBenefitPlanCashMember_f5ad43fd-398b-4602-a424-76bae813be6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_8f0273e8-8423-4d4b-bb44-4fcfb1fe2d69" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_6e7c3e46-7bb5-4e5b-9da2-b28183dd2390" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_8f0273e8-8423-4d4b-bb44-4fcfb1fe2d69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_4610627c-d1bc-4bb1-97b5-7c2bed5f2829" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanEquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_6e7c3e46-7bb5-4e5b-9da2-b28183dd2390" xlink:to="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_4610627c-d1bc-4bb1-97b5-7c2bed5f2829" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/EmployeeBenefitPlansReturnonCurrentandTargetAssetAllocationDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#EmployeeBenefitPlansReturnonCurrentandTargetAssetAllocationDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/EmployeeBenefitPlansReturnonCurrentandTargetAssetAllocationDetails" xlink:type="extended" id="i48e74cec181d4b3a8e63fcda32af928c_EmployeeBenefitPlansReturnonCurrentandTargetAssetAllocationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_60104a89-7573-4211-ab85-073a2da7bc54" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsInvestmentWithinPlanAssetCategoryAmount_a8944059-ebdc-48d6-9102-0726e634b74d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanPlanAssetsInvestmentWithinPlanAssetCategoryAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_60104a89-7573-4211-ab85-073a2da7bc54" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsInvestmentWithinPlanAssetCategoryAmount_a8944059-ebdc-48d6-9102-0726e634b74d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedBenefitPlanFairValueofPlanAssetsNotIncludingPooledFunds_1b751db9-5800-4c87-a7fd-a9fffaa018f3" xlink:href="dco-20221231.xsd#dco_DefinedBenefitPlanFairValueofPlanAssetsNotIncludingPooledFunds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_60104a89-7573-4211-ab85-073a2da7bc54" xlink:to="loc_dco_DefinedBenefitPlanFairValueofPlanAssetsNotIncludingPooledFunds_1b751db9-5800-4c87-a7fd-a9fffaa018f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedBenefitPlanFairValueofPooledFunds_1791dc2b-338d-476b-a32b-9ba03f23e108" xlink:href="dco-20221231.xsd#dco_DefinedBenefitPlanFairValueofPooledFunds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_60104a89-7573-4211-ab85-073a2da7bc54" xlink:to="loc_dco_DefinedBenefitPlanFairValueofPooledFunds_1791dc2b-338d-476b-a32b-9ba03f23e108" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_75898d9d-67e2-4906-800d-a99547bcf577" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_60104a89-7573-4211-ab85-073a2da7bc54" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_75898d9d-67e2-4906-800d-a99547bcf577" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_558de0be-d5ab-486d-bacf-e42971e36f00" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_60104a89-7573-4211-ab85-073a2da7bc54" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_558de0be-d5ab-486d-bacf-e42971e36f00" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_906fbc2d-c46e-4582-8ea5-f87032768e57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_558de0be-d5ab-486d-bacf-e42971e36f00" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_906fbc2d-c46e-4582-8ea5-f87032768e57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_906fbc2d-c46e-4582-8ea5-f87032768e57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_906fbc2d-c46e-4582-8ea5-f87032768e57" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_906fbc2d-c46e-4582-8ea5-f87032768e57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cfd6faa2-d9cc-425c-8247-c2ec91e93fb6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_906fbc2d-c46e-4582-8ea5-f87032768e57" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cfd6faa2-d9cc-425c-8247-c2ec91e93fb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_e23853c8-f2c8-4983-83ef-03cef93d3899" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cfd6faa2-d9cc-425c-8247-c2ec91e93fb6" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_e23853c8-f2c8-4983-83ef-03cef93d3899" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_1e9c1333-1409-4f12-bd98-d5e2c1a32694" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cfd6faa2-d9cc-425c-8247-c2ec91e93fb6" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_1e9c1333-1409-4f12-bd98-d5e2c1a32694" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_9716c73d-2273-4fea-96f4-476c09bbbdcb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_cfd6faa2-d9cc-425c-8247-c2ec91e93fb6" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_9716c73d-2273-4fea-96f4-476c09bbbdcb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8908e1dd-c663-4137-9ef7-5065ce64a543" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_558de0be-d5ab-486d-bacf-e42971e36f00" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8908e1dd-c663-4137-9ef7-5065ce64a543" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_8908e1dd-c663-4137-9ef7-5065ce64a543_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8908e1dd-c663-4137-9ef7-5065ce64a543" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_8908e1dd-c663-4137-9ef7-5065ce64a543_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_a91ca9dc-3985-45df-b26c-2a970f01e945" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_8908e1dd-c663-4137-9ef7-5065ce64a543" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_a91ca9dc-3985-45df-b26c-2a970f01e945" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_9002c142-e185-4cb4-9c53-4ba1c25ab965" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_a91ca9dc-3985-45df-b26c-2a970f01e945" xlink:to="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_9002c142-e185-4cb4-9c53-4ba1c25ab965" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_d081ce05-1105-4010-9063-a49545e6d785" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_a91ca9dc-3985-45df-b26c-2a970f01e945" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_d081ce05-1105-4010-9063-a49545e6d785" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_1551009d-5f22-4ceb-b591-9e572d01bb8a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanEquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_a91ca9dc-3985-45df-b26c-2a970f01e945" xlink:to="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_1551009d-5f22-4ceb-b591-9e572d01bb8a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedBenefitPlanOtherInvestmentsMember_2afa7cc2-a504-43e9-8cb8-41bd5daee653" xlink:href="dco-20221231.xsd#dco_DefinedBenefitPlanOtherInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_a91ca9dc-3985-45df-b26c-2a970f01e945" xlink:to="loc_dco_DefinedBenefitPlanOtherInvestmentsMember_2afa7cc2-a504-43e9-8cb8-41bd5daee653" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/EmployeeBenefitPlansWeightedaverageAssumptionsUsedtoDetermineBenefitObligationsDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#EmployeeBenefitPlansWeightedaverageAssumptionsUsedtoDetermineBenefitObligationsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/EmployeeBenefitPlansWeightedaverageAssumptionsUsedtoDetermineBenefitObligationsDetails" xlink:type="extended" id="i20693cc51c714bc097c0412b30b0996f_EmployeeBenefitPlansWeightedaverageAssumptionsUsedtoDetermineBenefitObligationsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsLineItems_3da2de98-bdb1-4936-90e4-9ca409a0d995" xlink:href="dco-20221231.xsd#dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_83d9c10b-5ee3-464a-befc-1823222804a9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsLineItems_3da2de98-bdb1-4936-90e4-9ca409a0d995" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_83d9c10b-5ee3-464a-befc-1823222804a9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate_7df0331a-c022-4234-8b52-b0e07d6b9682" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssumptionsUsedInCalculatingNetPeriodicBenefitCostAbstract_83d9c10b-5ee3-464a-befc-1823222804a9" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate_7df0331a-c022-4234-8b52-b0e07d6b9682" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedInCalculationsAbstract_5b6d5e62-b27f-4d01-adf0-418df0b49ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedInCalculationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsLineItems_3da2de98-bdb1-4936-90e4-9ca409a0d995" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedInCalculationsAbstract_5b6d5e62-b27f-4d01-adf0-418df0b49ad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate_f6bf4d9f-e65c-4f81-800e-927c454960f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedInCalculationsAbstract_5b6d5e62-b27f-4d01-adf0-418df0b49ad6" xlink:to="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate_f6bf4d9f-e65c-4f81-800e-927c454960f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationExpectedLongTermReturnOnAssets_63411f25-5232-421b-90e3-7d8a56f07481" xlink:href="dco-20221231.xsd#dco_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationExpectedLongTermReturnOnAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanAssumptionsUsedInCalculationsAbstract_5b6d5e62-b27f-4d01-adf0-418df0b49ad6" xlink:to="loc_dco_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationExpectedLongTermReturnOnAssets_63411f25-5232-421b-90e3-7d8a56f07481" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsTable_ab818fee-67aa-44ca-8493-50696c04a909" xlink:href="dco-20221231.xsd#dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsLineItems_3da2de98-bdb1-4936-90e4-9ca409a0d995" xlink:to="loc_dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsTable_ab818fee-67aa-44ca-8493-50696c04a909" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_4290ac32-4754-489e-b6f1-846e2a45bdd5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_ScheduleOfBenefitObligationsWeightedAverageAssumptionsTable_ab818fee-67aa-44ca-8493-50696c04a909" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_4290ac32-4754-489e-b6f1-846e2a45bdd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_4290ac32-4754-489e-b6f1-846e2a45bdd5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_4290ac32-4754-489e-b6f1-846e2a45bdd5" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_4290ac32-4754-489e-b6f1-846e2a45bdd5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_eac5a568-e87e-4df9-b72e-2c366cc8b6ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_4290ac32-4754-489e-b6f1-846e2a45bdd5" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_eac5a568-e87e-4df9-b72e-2c366cc8b6ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_19419308-ed79-4c7a-926f-bcef86f56ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_eac5a568-e87e-4df9-b72e-2c366cc8b6ed" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_19419308-ed79-4c7a-926f-bcef86f56ccc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_0bb38380-19be-4bb4-ada1-87fe5f09be11" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_eac5a568-e87e-4df9-b72e-2c366cc8b6ed" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_0bb38380-19be-4bb4-ada1-87fe5f09be11" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/EmployeeBenefitPlansFutureBenefitPaymentsUnderPensionPlansDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#EmployeeBenefitPlansFutureBenefitPaymentsUnderPensionPlansDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/EmployeeBenefitPlansFutureBenefitPaymentsUnderPensionPlansDetails" xlink:type="extended" id="ida2cd73d38724aa1b6bfd69cc42c360c_EmployeeBenefitPlansFutureBenefitPaymentsUnderPensionPlansDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_1b226978-b421-4add-8c96-a94d086dc7a4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_1b226978-b421-4add-8c96-a94d086dc7a4" xlink:to="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths_c82deb08-f51c-4b50-9c63-ed2458a0cf4a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths_c82deb08-f51c-4b50-9c63-ed2458a0cf4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo_bc96fd48-5801-4758-9b29-c133100b66ae" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo_bc96fd48-5801-4758-9b29-c133100b66ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree_d038393f-7086-4909-a993-b743eeb9dce0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree_d038393f-7086-4909-a993-b743eeb9dce0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour_0add1a06-53bc-4269-82c0-89e0fa9cb5a9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour_0add1a06-53bc-4269-82c0-89e0fa9cb5a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive_640152a5-0858-49ff-8708-2960d01d9f85" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive_640152a5-0858-49ff-8708-2960d01d9f85" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter_07b8f303-c966-49b1-b96e-e1717c039c88" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract_64b387cc-4f41-4216-9778-532376819608" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter_07b8f303-c966-49b1-b96e-e1717c039c88" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_0aec92d6-20fc-4359-90cf-a6d112c80209" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems_1b226978-b421-4add-8c96-a94d086dc7a4" xlink:to="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_0aec92d6-20fc-4359-90cf-a6d112c80209" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_ec39b3b0-7b6d-4fd2-ba5e-3b9d590359c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable_0aec92d6-20fc-4359-90cf-a6d112c80209" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_ec39b3b0-7b6d-4fd2-ba5e-3b9d590359c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_ec39b3b0-7b6d-4fd2-ba5e-3b9d590359c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_ec39b3b0-7b6d-4fd2-ba5e-3b9d590359c2" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_ec39b3b0-7b6d-4fd2-ba5e-3b9d590359c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_a0c74403-78af-4131-8049-cdc7bd2ae924" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_ec39b3b0-7b6d-4fd2-ba5e-3b9d590359c2" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_a0c74403-78af-4131-8049-cdc7bd2ae924" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PensionPlansDefinedBenefitMember_4ca34291-334f-4c36-bdf4-2c02e7d120ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_a0c74403-78af-4131-8049-cdc7bd2ae924" xlink:to="loc_us-gaap_PensionPlansDefinedBenefitMember_4ca34291-334f-4c36-bdf4-2c02e7d120ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_14fb3cc3-f3ef-4846-b0ed-8e1ea2b41ba1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_a0c74403-78af-4131-8049-cdc7bd2ae924" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_14fb3cc3-f3ef-4846-b0ed-8e1ea2b41ba1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended" id="i780d11bde3bd4d4eb40be45a071377c2_IncomeTaxesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount_2e448254-ca40-4bf5-afc1-c8d5c60dd09e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount_2e448254-ca40-4bf5-afc1-c8d5c60dd09e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_ba01d27b-8e7f-472a-8ce1-c1327ecc6b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_OperatingLossCarryforwards_ba01d27b-8e7f-472a-8ce1-c1327ecc6b7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_OperatingLossCarryforwardNotExpectedtobeRealized_1e309a56-873e-458f-972d-efcbc115f41a" xlink:href="dco-20221231.xsd#dco_OperatingLossCarryforwardNotExpectedtobeRealized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_dco_OperatingLossCarryforwardNotExpectedtobeRealized_1e309a56-873e-458f-972d-efcbc115f41a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_67fec580-3647-48db-aca8-41237082761e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsTaxCreditCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxCreditCarryforwards_67fec580-3647-48db-aca8-41237082761e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_d71f2609-bd8d-4210-a94a-497dca834265" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_d71f2609-bd8d-4210-a94a-497dca834265" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefits_fd3a2ac4-ce27-48d7-bce1-2870ea7cbab7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrecognizedTaxBenefits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_UnrecognizedTaxBenefits_fd3a2ac4-ce27-48d7-bce1-2870ea7cbab7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_e801ecae-6bb6-4fb3-bb50-dea8ee749b7f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_e801ecae-6bb6-4fb3-bb50-dea8ee749b7f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_6d9d43e2-73a3-4058-8a23-fe7c101573b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_6d9d43e2-73a3-4058-8a23-fe7c101573b6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther_08ce0c03-5549-4864-b3f7-eb15ef0fdae1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther_08ce0c03-5549-4864-b3f7-eb15ef0fdae1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpense_38763b1b-6efd-4f4f-98d4-6eeedb565dd8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpense_38763b1b-6efd-4f4f-98d4-6eeedb565dd8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_3ff59ab3-6ec3-4262-a4eb-1a010b77a96b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable_3ff59ab3-6ec3-4262-a4eb-1a010b77a96b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardTable_7cd958b8-f655-4b2c-8ce0-f872d184be2a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TaxCreditCarryforwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TaxCreditCarryforwardLineItems_ce2833bf-95db-4310-b8f5-73c229857bc9" xlink:to="loc_us-gaap_TaxCreditCarryforwardTable_7cd958b8-f655-4b2c-8ce0-f872d184be2a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_230a97e2-743a-4709-ba54-6321aaf11242" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TaxCreditCarryforwardTable_7cd958b8-f655-4b2c-8ce0-f872d184be2a" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_230a97e2-743a-4709-ba54-6321aaf11242" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_230a97e2-743a-4709-ba54-6321aaf11242_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_230a97e2-743a-4709-ba54-6321aaf11242" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_230a97e2-743a-4709-ba54-6321aaf11242_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_73a5e5a2-802c-4760-8884-0aa63c8f9db8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_230a97e2-743a-4709-ba54-6321aaf11242" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_73a5e5a2-802c-4760-8884-0aa63c8f9db8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_3bdf1f88-890f-4d41-ae9f-5152e6586ec0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_73a5e5a2-802c-4760-8884-0aa63c8f9db8" xlink:to="loc_us-gaap_DomesticCountryMember_3bdf1f88-890f-4d41-ae9f-5152e6586ec0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_bd9c058e-12c6-44bb-9b15-c1571e7760f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_73a5e5a2-802c-4760-8884-0aa63c8f9db8" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_bd9c058e-12c6-44bb-9b15-c1571e7760f3" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="i9b956db20c1b4829826be9ae55bef7e2_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationReserve_80c84c21-7015-4bf6-8733-fe1f7261f7d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LitigationReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_LitigationReserve_80c84c21-7015-4bf6-8733-fe1f7261f7d2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease_cd472f5d-17a6-43be-afd7-8acd32701fb1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease_cd472f5d-17a6-43be-afd7-8acd32701fb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLegalSettlements_3f84cb85-142f-415c-a240-2c6975f1316f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_PaymentsForLegalSettlements_3f84cb85-142f-415c-a240-2c6975f1316f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_9944af7b-0ed4-4c8f-92fe-cace1bf4d5a7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_9944af7b-0ed4-4c8f-92fe-cace1bf4d5a7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_d795a64c-badf-4309-985b-e7e97ab91880" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_d795a64c-badf-4309-985b-e7e97ab91880" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LossContingencyNumberOfBuildingsAffected_655ea86d-0487-4172-9301-bdcf261c4183" xlink:href="dco-20221231.xsd#dco_LossContingencyNumberOfBuildingsAffected"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_dco_LossContingencyNumberOfBuildingsAffected_655ea86d-0487-4172-9301-bdcf261c4183" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AreaOfRealEstateProperty_da51401b-2d75-40ed-a22c-be3d026a409b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AreaOfRealEstateProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_AreaOfRealEstateProperty_da51401b-2d75-40ed-a22c-be3d026a409b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f11ae3e3-5026-4bb3-97e9-0fd077b19c7e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f11ae3e3-5026-4bb3-97e9-0fd077b19c7e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_1e86afc3-9fbb-4eca-a1a7-41e4992b94f1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_1e86afc3-9fbb-4eca-a1a7-41e4992b94f1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleCarryingValueOfAsset_e367a1e1-686e-4188-85c4-13f2311bce23" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleCarryingValueOfAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleCarryingValueOfAsset_e367a1e1-686e-4188-85c4-13f2311bce23" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyReceivableProceeds_e7b5f8e9-87b8-48bf-ba1a-784b5cd43de6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyReceivableProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_LossContingencyReceivableProceeds_e7b5f8e9-87b8-48bf-ba1a-784b5cd43de6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_54d8d86a-1047-4ff9-804c-0798229cc5c2" xlink:to="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_fad87696-db8c-461e-99ca-f754836cdd2d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_fad87696-db8c-461e-99ca-f754836cdd2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_fad87696-db8c-461e-99ca-f754836cdd2d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_fad87696-db8c-461e-99ca-f754836cdd2d" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_fad87696-db8c-461e-99ca-f754836cdd2d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_fad54242-19a0-4a91-835d-cf604b2df2d9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_fad87696-db8c-461e-99ca-f754836cdd2d" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_fad54242-19a0-4a91-835d-cf604b2df2d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesMember_fc4bb71d-3496-4b0f-81eb-2a1002ed87fd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_fad54242-19a0-4a91-835d-cf604b2df2d9" xlink:to="loc_us-gaap_AccruedLiabilitiesMember_fc4bb71d-3496-4b0f-81eb-2a1002ed87fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_17e26be1-e6cb-4ab4-a0ac-a7a587d5f323" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_17e26be1-e6cb-4ab4-a0ac-a7a587d5f323" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_17e26be1-e6cb-4ab4-a0ac-a7a587d5f323_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_17e26be1-e6cb-4ab4-a0ac-a7a587d5f323" xlink:to="loc_us-gaap_SegmentDomain_17e26be1-e6cb-4ab4-a0ac-a7a587d5f323_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_404b9267-d82d-4d44-a7db-b90ea7cbfa37" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_17e26be1-e6cb-4ab4-a0ac-a7a587d5f323" xlink:to="loc_us-gaap_SegmentDomain_404b9267-d82d-4d44-a7db-b90ea7cbfa37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_0472a5e8-053a-4698-bc6d-799b6e8cad78" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_404b9267-d82d-4d44-a7db-b90ea7cbfa37" xlink:to="loc_dco_StructuralSystemsSegmentMember_0472a5e8-053a-4698-bc6d-799b6e8cad78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_f8d99854-d9e3-4498-a8a6-2b15b656ffb2" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_srt_StatementGeographicalAxis_f8d99854-d9e3-4498-a8a6-2b15b656ffb2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_f8d99854-d9e3-4498-a8a6-2b15b656ffb2_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_f8d99854-d9e3-4498-a8a6-2b15b656ffb2" xlink:to="loc_srt_SegmentGeographicalDomain_f8d99854-d9e3-4498-a8a6-2b15b656ffb2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_93690fb3-9cef-4e5d-af08-e199bae38ba9" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_f8d99854-d9e3-4498-a8a6-2b15b656ffb2" xlink:to="loc_srt_SegmentGeographicalDomain_93690fb3-9cef-4e5d-af08-e199bae38ba9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LocationOneMember_d040eefd-5fd2-489d-aa56-63c845a89ed2" xlink:href="dco-20221231.xsd#dco_LocationOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_93690fb3-9cef-4e5d-af08-e199bae38ba9" xlink:to="loc_dco_LocationOneMember_d040eefd-5fd2-489d-aa56-63c845a89ed2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LocationTwoMember_3b4e542d-138d-4f79-aca1-71071e30d6dc" xlink:href="dco-20221231.xsd#dco_LocationTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_93690fb3-9cef-4e5d-af08-e199bae38ba9" xlink:to="loc_dco_LocationTwoMember_3b4e542d-138d-4f79-aca1-71071e30d6dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GuaymasMexicoMember_7e13dfa5-a466-4a69-b0ed-bbd25e6a88d2" xlink:href="dco-20221231.xsd#dco_GuaymasMexicoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_93690fb3-9cef-4e5d-af08-e199bae38ba9" xlink:to="loc_dco_GuaymasMexicoMember_7e13dfa5-a466-4a69-b0ed-bbd25e6a88d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b397d122-b768-4ada-b6ef-f9b0c75a3eec" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_srt_RangeAxis_b397d122-b768-4ada-b6ef-f9b0c75a3eec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b397d122-b768-4ada-b6ef-f9b0c75a3eec_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b397d122-b768-4ada-b6ef-f9b0c75a3eec" xlink:to="loc_srt_RangeMember_b397d122-b768-4ada-b6ef-f9b0c75a3eec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1f55bd57-abfa-4e3d-8227-7dc3deb85a9e" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b397d122-b768-4ada-b6ef-f9b0c75a3eec" xlink:to="loc_srt_RangeMember_1f55bd57-abfa-4e3d-8227-7dc3deb85a9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_a78d5463-3c18-4582-b5b6-888c9e2c0d7c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1f55bd57-abfa-4e3d-8227-7dc3deb85a9e" xlink:to="loc_srt_MinimumMember_a78d5463-3c18-4582-b5b6-888c9e2c0d7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_697b98a8-8a50-4d3b-b004-e9434f121523" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1f55bd57-abfa-4e3d-8227-7dc3deb85a9e" xlink:to="loc_srt_MaximumMember_697b98a8-8a50-4d3b-b004-e9434f121523" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_6f7c41bf-5d11-4dfe-b9d3-f024babfea1e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_6f7c41bf-5d11-4dfe-b9d3-f024babfea1e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_6f7c41bf-5d11-4dfe-b9d3-f024babfea1e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_6f7c41bf-5d11-4dfe-b9d3-f024babfea1e" xlink:to="loc_us-gaap_LossContingencyNatureDomain_6f7c41bf-5d11-4dfe-b9d3-f024babfea1e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_20319063-ed67-4575-b3a1-351e4b70f034" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_6f7c41bf-5d11-4dfe-b9d3-f024babfea1e" xlink:to="loc_us-gaap_LossContingencyNatureDomain_20319063-ed67-4575-b3a1-351e4b70f034" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DamageFromFireExplosionOrOtherHazardMember_aaa35170-ee7b-45ab-bc3b-e2a5fa9be570" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DamageFromFireExplosionOrOtherHazardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_20319063-ed67-4575-b3a1-351e4b70f034" xlink:to="loc_us-gaap_DamageFromFireExplosionOrOtherHazardMember_aaa35170-ee7b-45ab-bc3b-e2a5fa9be570" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_9b20450a-02cf-4cd3-87c4-48d94d7d266d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_srt_RestatementAxis_9b20450a-02cf-4cd3-87c4-48d94d7d266d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_9b20450a-02cf-4cd3-87c4-48d94d7d266d_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_9b20450a-02cf-4cd3-87c4-48d94d7d266d" xlink:to="loc_srt_RestatementDomain_9b20450a-02cf-4cd3-87c4-48d94d7d266d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_78238256-cadb-4af7-b971-7f9ba01328b5" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_9b20450a-02cf-4cd3-87c4-48d94d7d266d" xlink:to="loc_srt_RestatementDomain_78238256-cadb-4af7-b971-7f9ba01328b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RevisionOfPriorPeriodReclassificationAdjustmentMember_ab9edd6d-fbee-4087-8de7-e0e1a7bda8e1" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RevisionOfPriorPeriodReclassificationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_78238256-cadb-4af7-b971-7f9ba01328b5" xlink:to="loc_srt_RevisionOfPriorPeriodReclassificationAdjustmentMember_ab9edd6d-fbee-4087-8de7-e0e1a7bda8e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_b1ed1565-d3dc-45f7-9b76-300d8c33c13a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_b1ed1565-d3dc-45f7-9b76-300d8c33c13a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_b1ed1565-d3dc-45f7-9b76-300d8c33c13a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_b1ed1565-d3dc-45f7-9b76-300d8c33c13a" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_b1ed1565-d3dc-45f7-9b76-300d8c33c13a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a0e1bec3-74fd-4d9a-b97f-86c21381dd18" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_b1ed1565-d3dc-45f7-9b76-300d8c33c13a" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a0e1bec3-74fd-4d9a-b97f-86c21381dd18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentMember_4772b617-88d2-4e0b-adec-b4ff243c980c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a0e1bec3-74fd-4d9a-b97f-86c21381dd18" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentMember_4772b617-88d2-4e0b-adec-b4ff243c980c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoriesMember_f9d0135f-4d41-40e6-91d1-c29791a1dad0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_a0e1bec3-74fd-4d9a-b97f-86c21381dd18" xlink:to="loc_us-gaap_InventoriesMember_f9d0135f-4d41-40e6-91d1-c29791a1dad0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_307ab54f-5a32-49b0-b3b9-b2dd48c4b933" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_f2961e49-4be7-496f-aa68-671ec8e04e54" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_307ab54f-5a32-49b0-b3b9-b2dd48c4b933" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_307ab54f-5a32-49b0-b3b9-b2dd48c4b933_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_307ab54f-5a32-49b0-b3b9-b2dd48c4b933" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_307ab54f-5a32-49b0-b3b9-b2dd48c4b933_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_bcbf001d-6467-4b98-91fd-a1ea06276973" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_307ab54f-5a32-49b0-b3b9-b2dd48c4b933" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_bcbf001d-6467-4b98-91fd-a1ea06276973" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_0538a2dd-efeb-437f-9bac-a061da28c49f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_bcbf001d-6467-4b98-91fd-a1ea06276973" xlink:to="loc_us-gaap_SubsequentEventMember_0538a2dd-efeb-437f-9bac-a061da28c49f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/MajorCustomersandConcentrationsofCreditRiskSalestoMajorCustomersDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#MajorCustomersandConcentrationsofCreditRiskSalestoMajorCustomersDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/MajorCustomersandConcentrationsofCreditRiskSalestoMajorCustomersDetails" xlink:type="extended" id="iade9779b25dc44e48f43df334fd1e057_MajorCustomersandConcentrationsofCreditRiskSalestoMajorCustomersDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_4bfcd859-a8cc-4128-bfc0-4a26857ddba2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EntityWideRevenueMajorCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_c791d8a9-3be3-466e-b831-0a6370af792e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_4bfcd859-a8cc-4128-bfc0-4a26857ddba2" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_c791d8a9-3be3-466e-b831-0a6370af792e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_6a12f98a-453f-4c74-95a6-31d86adfbb7c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_4bfcd859-a8cc-4128-bfc0-4a26857ddba2" xlink:to="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_6a12f98a-453f-4c74-95a6-31d86adfbb7c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_fedb7985-6515-447b-8ca3-4511c908c4e9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_6a12f98a-453f-4c74-95a6-31d86adfbb7c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_fedb7985-6515-447b-8ca3-4511c908c4e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_fedb7985-6515-447b-8ca3-4511c908c4e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_fedb7985-6515-447b-8ca3-4511c908c4e9" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_fedb7985-6515-447b-8ca3-4511c908c4e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_deff02b6-125d-415e-b6cb-2e29c3397399" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_fedb7985-6515-447b-8ca3-4511c908c4e9" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_deff02b6-125d-415e-b6cb-2e29c3397399" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_7779923d-938c-49b6-8202-768da0fdbc42" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_deff02b6-125d-415e-b6cb-2e29c3397399" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_7779923d-938c-49b6-8202-768da0fdbc42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_e8b2445c-da27-4e8f-80ad-f08e7e1b1977" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_6a12f98a-453f-4c74-95a6-31d86adfbb7c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_e8b2445c-da27-4e8f-80ad-f08e7e1b1977" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e8b2445c-da27-4e8f-80ad-f08e7e1b1977_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_e8b2445c-da27-4e8f-80ad-f08e7e1b1977" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e8b2445c-da27-4e8f-80ad-f08e7e1b1977_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fad83bb6-81ab-4f74-acfe-cd8132eccfc3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_e8b2445c-da27-4e8f-80ad-f08e7e1b1977" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fad83bb6-81ab-4f74-acfe-cd8132eccfc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_88600380-971d-444c-80c6-fa2246711cfe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fad83bb6-81ab-4f74-acfe-cd8132eccfc3" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_88600380-971d-444c-80c6-fa2246711cfe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_ab78487e-9b16-4ee6-835d-6825c6e71498" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_6a12f98a-453f-4c74-95a6-31d86adfbb7c" xlink:to="loc_srt_MajorCustomersAxis_ab78487e-9b16-4ee6-835d-6825c6e71498" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_ab78487e-9b16-4ee6-835d-6825c6e71498_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_ab78487e-9b16-4ee6-835d-6825c6e71498" xlink:to="loc_srt_NameOfMajorCustomerDomain_ab78487e-9b16-4ee6-835d-6825c6e71498_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_ab78487e-9b16-4ee6-835d-6825c6e71498" xlink:to="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BoeingMember_0c920f86-0101-405d-be93-83c8e51f1cb7" xlink:href="dco-20221231.xsd#dco_BoeingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_BoeingMember_0c920f86-0101-405d-be93-83c8e51f1cb7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GeneralDynamicsCorporationMember_aa306741-6b07-4bfd-9d15-b1dd51fe1517" xlink:href="dco-20221231.xsd#dco_GeneralDynamicsCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_GeneralDynamicsCorporationMember_aa306741-6b07-4bfd-9d15-b1dd51fe1517" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LockheedMartinMember_c19f6662-222f-4e22-88bd-1bea49c7a23e" xlink:href="dco-20221231.xsd#dco_LockheedMartinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_LockheedMartinMember_c19f6662-222f-4e22-88bd-1bea49c7a23e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NorthropMember_7c4e0da1-9e7a-4616-8821-ac552ae9e72b" xlink:href="dco-20221231.xsd#dco_NorthropMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_NorthropMember_7c4e0da1-9e7a-4616-8821-ac552ae9e72b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_RaytheonCompanyMember_a1196a97-f0a6-4c8a-a305-ae1040878704" xlink:href="dco-20221231.xsd#dco_RaytheonCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_RaytheonCompanyMember_a1196a97-f0a6-4c8a-a305-ae1040878704" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SpiritAerosystemsMember_a7414598-52ab-465a-9c27-57332b8a26db" xlink:href="dco-20221231.xsd#dco_SpiritAerosystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_SpiritAerosystemsMember_a7414598-52ab-465a-9c27-57332b8a26db" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ViasatIncMember_a0ad2d2c-7096-48ee-920f-7b602eaf25e6" xlink:href="dco-20221231.xsd#dco_ViasatIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_ViasatIncMember_a0ad2d2c-7096-48ee-920f-7b602eaf25e6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_TopTenCustomersMember_468c02be-c16d-4540-897f-ea345253c1c9" xlink:href="dco-20221231.xsd#dco_TopTenCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1efbe9b0-20b7-44af-be9a-bb16f84672bd" xlink:to="loc_dco_TopTenCustomersMember_468c02be-c16d-4540-897f-ea345253c1c9" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/MajorCustomersandConcentrationsofCreditRiskReceivablesfromCustomersDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#MajorCustomersandConcentrationsofCreditRiskReceivablesfromCustomersDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/MajorCustomersandConcentrationsofCreditRiskReceivablesfromCustomersDetails" xlink:type="extended" id="i173ec0381a974e07b48d8386e5c80f07_MajorCustomersandConcentrationsofCreditRiskReceivablesfromCustomersDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_0fff8c8e-3962-451e-84d1-a1922723aeea" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_886f090d-9b10-4c5a-bda5-0f4782eae170" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_0fff8c8e-3962-451e-84d1-a1922723aeea" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_886f090d-9b10-4c5a-bda5-0f4782eae170" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_8ca4fcc0-43f0-42c3-a1d5-febcf8c6991c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_0fff8c8e-3962-451e-84d1-a1922723aeea" xlink:to="loc_us-gaap_ConcentrationRiskTable_8ca4fcc0-43f0-42c3-a1d5-febcf8c6991c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_56c98ed6-9633-4a46-8fac-820c70a9b192" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_8ca4fcc0-43f0-42c3-a1d5-febcf8c6991c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_56c98ed6-9633-4a46-8fac-820c70a9b192" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_56c98ed6-9633-4a46-8fac-820c70a9b192_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_56c98ed6-9633-4a46-8fac-820c70a9b192" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_56c98ed6-9633-4a46-8fac-820c70a9b192_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_5d28f19e-405e-4dd4-a319-91aa9e617997" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_56c98ed6-9633-4a46-8fac-820c70a9b192" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_5d28f19e-405e-4dd4-a319-91aa9e617997" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_90c9b8c9-ff9e-4c76-987f-6c62d95e16c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_5d28f19e-405e-4dd4-a319-91aa9e617997" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_90c9b8c9-ff9e-4c76-987f-6c62d95e16c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d83d5c25-2af6-422e-bd5b-6c0e1f76c47e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_8ca4fcc0-43f0-42c3-a1d5-febcf8c6991c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d83d5c25-2af6-422e-bd5b-6c0e1f76c47e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d83d5c25-2af6-422e-bd5b-6c0e1f76c47e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d83d5c25-2af6-422e-bd5b-6c0e1f76c47e" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d83d5c25-2af6-422e-bd5b-6c0e1f76c47e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d3cc7e34-7e10-4c5e-b77c-fa24e8540579" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_d83d5c25-2af6-422e-bd5b-6c0e1f76c47e" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d3cc7e34-7e10-4c5e-b77c-fa24e8540579" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_b2b1d281-c8bd-417b-977f-a57fecda9970" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_d3cc7e34-7e10-4c5e-b77c-fa24e8540579" xlink:to="loc_us-gaap_AccountsReceivableMember_b2b1d281-c8bd-417b-977f-a57fecda9970" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_22f4d7e7-ea18-428f-b2cf-40077dfbf1ba" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_8ca4fcc0-43f0-42c3-a1d5-febcf8c6991c" xlink:to="loc_srt_MajorCustomersAxis_22f4d7e7-ea18-428f-b2cf-40077dfbf1ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_22f4d7e7-ea18-428f-b2cf-40077dfbf1ba_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_22f4d7e7-ea18-428f-b2cf-40077dfbf1ba" xlink:to="loc_srt_NameOfMajorCustomerDomain_22f4d7e7-ea18-428f-b2cf-40077dfbf1ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_22f4d7e7-ea18-428f-b2cf-40077dfbf1ba" xlink:to="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BoeingMember_3b14eaa0-7e01-41f0-a22b-1b428815e426" xlink:href="dco-20221231.xsd#dco_BoeingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:to="loc_dco_BoeingMember_3b14eaa0-7e01-41f0-a22b-1b428815e426" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GeneralDynamicsCorporationMember_40477198-3211-4e14-99ea-98f21cde58e2" xlink:href="dco-20221231.xsd#dco_GeneralDynamicsCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:to="loc_dco_GeneralDynamicsCorporationMember_40477198-3211-4e14-99ea-98f21cde58e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LockheedMartinMember_feb77e50-bcd6-4f37-a4c9-da5c93448400" xlink:href="dco-20221231.xsd#dco_LockheedMartinMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:to="loc_dco_LockheedMartinMember_feb77e50-bcd6-4f37-a4c9-da5c93448400" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NorthropMember_a71c2c41-74bf-4c23-8e47-06a4d4243aa2" xlink:href="dco-20221231.xsd#dco_NorthropMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:to="loc_dco_NorthropMember_a71c2c41-74bf-4c23-8e47-06a4d4243aa2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_RaytheonCompanyMember_7d677cd1-5d3a-4d79-bf7a-68863872774e" xlink:href="dco-20221231.xsd#dco_RaytheonCompanyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:to="loc_dco_RaytheonCompanyMember_7d677cd1-5d3a-4d79-bf7a-68863872774e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SpiritAerosystemsMember_c71c5475-242f-4a2f-a7ca-be7ff8abe694" xlink:href="dco-20221231.xsd#dco_SpiritAerosystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:to="loc_dco_SpiritAerosystemsMember_c71c5475-242f-4a2f-a7ca-be7ff8abe694" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ViasatIncMember_85e9daf2-b1bd-42dd-8066-e65b8a5b5624" xlink:href="dco-20221231.xsd#dco_ViasatIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_6c82eca4-db11-48a1-bedc-558142fcf8ca" xlink:to="loc_dco_ViasatIncMember_85e9daf2-b1bd-42dd-8066-e65b8a5b5624" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/MajorCustomersandConcentrationsofCreditRiskNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#MajorCustomersandConcentrationsofCreditRiskNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/MajorCustomersandConcentrationsofCreditRiskNarrativeDetails" xlink:type="extended" id="ib4169d0e14e04dd9854c5126686961f5_MajorCustomersandConcentrationsofCreditRiskNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_e65acc68-cc6f-4d5c-8f30-8054f449f34e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_c26b34d8-aac0-4ad7-a565-82e5589ca2af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_e65acc68-cc6f-4d5c-8f30-8054f449f34e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_c26b34d8-aac0-4ad7-a565-82e5589ca2af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PercentageOfNetSales_77f51bf1-3a2b-4cbf-b660-eb7c3f7a93c8" xlink:href="dco-20221231.xsd#dco_PercentageOfNetSales"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_e65acc68-cc6f-4d5c-8f30-8054f449f34e" xlink:to="loc_dco_PercentageOfNetSales_77f51bf1-3a2b-4cbf-b660-eb7c3f7a93c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_75851929-50c4-429f-b8d9-2d5de7f0118b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_e65acc68-cc6f-4d5c-8f30-8054f449f34e" xlink:to="loc_us-gaap_ConcentrationRiskTable_75851929-50c4-429f-b8d9-2d5de7f0118b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1e7a2018-16a1-4150-9443-b1793795b23d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_75851929-50c4-429f-b8d9-2d5de7f0118b" xlink:to="loc_srt_RangeAxis_1e7a2018-16a1-4150-9443-b1793795b23d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1e7a2018-16a1-4150-9443-b1793795b23d_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1e7a2018-16a1-4150-9443-b1793795b23d" xlink:to="loc_srt_RangeMember_1e7a2018-16a1-4150-9443-b1793795b23d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f11acdb5-1d39-4e37-bdd6-e31bb7a6f581" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1e7a2018-16a1-4150-9443-b1793795b23d" xlink:to="loc_srt_RangeMember_f11acdb5-1d39-4e37-bdd6-e31bb7a6f581" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_2bbfa355-1718-4da7-9271-4ba411ae103e" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f11acdb5-1d39-4e37-bdd6-e31bb7a6f581" xlink:to="loc_srt_MaximumMember_2bbfa355-1718-4da7-9271-4ba411ae103e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_686ecd37-b261-43ce-b074-08568b5a244e" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_75851929-50c4-429f-b8d9-2d5de7f0118b" xlink:to="loc_srt_StatementGeographicalAxis_686ecd37-b261-43ce-b074-08568b5a244e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_686ecd37-b261-43ce-b074-08568b5a244e_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_686ecd37-b261-43ce-b074-08568b5a244e" xlink:to="loc_srt_SegmentGeographicalDomain_686ecd37-b261-43ce-b074-08568b5a244e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_3f1d02f0-5e8e-42d0-a2c4-72e45532bf5c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_686ecd37-b261-43ce-b074-08568b5a244e" xlink:to="loc_srt_SegmentGeographicalDomain_3f1d02f0-5e8e-42d0-a2c4-72e45532bf5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_70eb0f46-2a84-4486-bffc-ee77020f1ec4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_3f1d02f0-5e8e-42d0-a2c4-72e45532bf5c" xlink:to="loc_us-gaap_NonUsMember_70eb0f46-2a84-4486-bffc-ee77020f1ec4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessSegmentInformationNarrativeDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#BusinessSegmentInformationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessSegmentInformationNarrativeDetails" xlink:type="extended" id="ic12f995b84104a16b38f8dbaf6d23a55_BusinessSegmentInformationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_80676b39-e151-4c64-ae87-f357bb1e0c01" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_dfa38abf-4fc1-4f4f-96e4-c86d55e03c02" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_80676b39-e151-4c64-ae87-f357bb1e0c01" xlink:to="loc_us-gaap_NumberOfReportableSegments_dfa38abf-4fc1-4f4f-96e4-c86d55e03c02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_66bf5831-4c3a-4dcd-be64-fa8b2cea8c7d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_80676b39-e151-4c64-ae87-f357bb1e0c01" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_66bf5831-4c3a-4dcd-be64-fa8b2cea8c7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_05f0e6a0-d5a7-461f-a9fc-9b4fb1bf2415" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_80676b39-e151-4c64-ae87-f357bb1e0c01" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_05f0e6a0-d5a7-461f-a9fc-9b4fb1bf2415" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_436ad8f5-f516-4314-9afc-bf7aa19ebb5f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_80676b39-e151-4c64-ae87-f357bb1e0c01" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_436ad8f5-f516-4314-9afc-bf7aa19ebb5f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_f40598cd-c798-44a2-9e2d-3f990f432a60" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_80676b39-e151-4c64-ae87-f357bb1e0c01" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_f40598cd-c798-44a2-9e2d-3f990f432a60" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_cbd01545-e89c-4d96-99c7-4cf1f9e598fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_f40598cd-c798-44a2-9e2d-3f990f432a60" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_cbd01545-e89c-4d96-99c7-4cf1f9e598fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cbd01545-e89c-4d96-99c7-4cf1f9e598fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_cbd01545-e89c-4d96-99c7-4cf1f9e598fa" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cbd01545-e89c-4d96-99c7-4cf1f9e598fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d1b6844b-1d31-412d-9ac1-c587452028b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_cbd01545-e89c-4d96-99c7-4cf1f9e598fa" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d1b6844b-1d31-412d-9ac1-c587452028b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_b75f82bc-74ec-49d5-aaee-42d4ad8b7a29" xlink:href="dco-20221231.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d1b6844b-1d31-412d-9ac1-c587452028b6" xlink:to="loc_dco_MagneticSealCorporationMember_b75f82bc-74ec-49d5-aaee-42d4ad8b7a29" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails" xlink:type="extended" id="i58ce46c60a514b78a4219d2cb92c2f17_BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_08009774-e391-43d7-a0ae-693a4a64450d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b4eef517-864a-461c-b1cc-294ad29bf44b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_08009774-e391-43d7-a0ae-693a4a64450d" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b4eef517-864a-461c-b1cc-294ad29bf44b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_12ef3561-43a7-4991-a969-d11189ee8b62" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_08009774-e391-43d7-a0ae-693a4a64450d" xlink:to="loc_us-gaap_OperatingIncomeLoss_12ef3561-43a7-4991-a969-d11189ee8b62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_d4cc7d2e-38a3-46b1-a1c7-d06a5d4a7626" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_08009774-e391-43d7-a0ae-693a4a64450d" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_d4cc7d2e-38a3-46b1-a1c7-d06a5d4a7626" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_161f7672-d618-430e-961f-62b8ec800c3c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_08009774-e391-43d7-a0ae-693a4a64450d" xlink:to="loc_us-gaap_DepreciationAndAmortization_161f7672-d618-430e-961f-62b8ec800c3c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_CapitalExpenditures_02772c17-0153-4df4-bb56-bfffa55b4d07" xlink:href="dco-20221231.xsd#dco_CapitalExpenditures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_08009774-e391-43d7-a0ae-693a4a64450d" xlink:to="loc_dco_CapitalExpenditures_02772c17-0153-4df4-bb56-bfffa55b4d07" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_854a2089-03b8-4fad-aedf-846f2e19acbf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_08009774-e391-43d7-a0ae-693a4a64450d" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_854a2089-03b8-4fad-aedf-846f2e19acbf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_df082a7d-e3f0-4bcd-9fb0-2bd16ba96b09" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_854a2089-03b8-4fad-aedf-846f2e19acbf" xlink:to="loc_srt_ConsolidationItemsAxis_df082a7d-e3f0-4bcd-9fb0-2bd16ba96b09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_df082a7d-e3f0-4bcd-9fb0-2bd16ba96b09_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_df082a7d-e3f0-4bcd-9fb0-2bd16ba96b09" xlink:to="loc_srt_ConsolidationItemsDomain_df082a7d-e3f0-4bcd-9fb0-2bd16ba96b09_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_80b3c504-b4b8-48db-972d-4062b2c9863c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_df082a7d-e3f0-4bcd-9fb0-2bd16ba96b09" xlink:to="loc_srt_ConsolidationItemsDomain_80b3c504-b4b8-48db-972d-4062b2c9863c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_766d0e75-376d-4fa0-a5de-24c7e749c172" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_80b3c504-b4b8-48db-972d-4062b2c9863c" xlink:to="loc_us-gaap_OperatingSegmentsMember_766d0e75-376d-4fa0-a5de-24c7e749c172" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_45f4323e-21b8-4cff-a15e-36cbd4389edf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_80b3c504-b4b8-48db-972d-4062b2c9863c" xlink:to="loc_us-gaap_CorporateNonSegmentMember_45f4323e-21b8-4cff-a15e-36cbd4389edf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_37e7ee42-4a76-4d06-ab84-666109a2b6a2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_854a2089-03b8-4fad-aedf-846f2e19acbf" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_37e7ee42-4a76-4d06-ab84-666109a2b6a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_37e7ee42-4a76-4d06-ab84-666109a2b6a2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_37e7ee42-4a76-4d06-ab84-666109a2b6a2" xlink:to="loc_us-gaap_SegmentDomain_37e7ee42-4a76-4d06-ab84-666109a2b6a2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_a48dbce0-788e-46a5-b585-3bc36ab977dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_37e7ee42-4a76-4d06-ab84-666109a2b6a2" xlink:to="loc_us-gaap_SegmentDomain_a48dbce0-788e-46a5-b585-3bc36ab977dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_ef2072ed-2f0a-4a29-8b33-84f1f9d04995" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_a48dbce0-788e-46a5-b585-3bc36ab977dc" xlink:to="loc_dco_ElectronicSystemsSegmentMember_ef2072ed-2f0a-4a29-8b33-84f1f9d04995" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_b471c8ce-d882-4f2d-8992-37f7dabf31f0" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_a48dbce0-788e-46a5-b585-3bc36ab977dc" xlink:to="loc_dco_StructuralSystemsSegmentMember_b471c8ce-d882-4f2d-8992-37f7dabf31f0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessSegmentInformationSegmentAssetsDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#BusinessSegmentInformationSegmentAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessSegmentInformationSegmentAssetsDetails" xlink:type="extended" id="i8230fe7c10bc41b3b9d16155a5ae972e_BusinessSegmentInformationSegmentAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_c89d9869-e7b3-4542-9b7a-77a237d82e89" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_47e0f333-9b3f-447d-87c9-20761d3c6a53" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c89d9869-e7b3-4542-9b7a-77a237d82e89" xlink:to="loc_us-gaap_Assets_47e0f333-9b3f-447d-87c9-20761d3c6a53" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GoodwillAndOtherIntangibleAssets_20332264-a384-4bb0-a6af-a9cb14c01ba8" xlink:href="dco-20221231.xsd#dco_GoodwillAndOtherIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c89d9869-e7b3-4542-9b7a-77a237d82e89" xlink:to="loc_dco_GoodwillAndOtherIntangibleAssets_20332264-a384-4bb0-a6af-a9cb14c01ba8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_a461176c-ac4f-456c-9a5f-00935990937d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c89d9869-e7b3-4542-9b7a-77a237d82e89" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_a461176c-ac4f-456c-9a5f-00935990937d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_ed499a6a-f64b-4a90-9c5e-c7c6030f2e85" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_a461176c-ac4f-456c-9a5f-00935990937d" xlink:to="loc_srt_ConsolidationItemsAxis_ed499a6a-f64b-4a90-9c5e-c7c6030f2e85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_ed499a6a-f64b-4a90-9c5e-c7c6030f2e85_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_ed499a6a-f64b-4a90-9c5e-c7c6030f2e85" xlink:to="loc_srt_ConsolidationItemsDomain_ed499a6a-f64b-4a90-9c5e-c7c6030f2e85_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_45f62cdf-afd8-43bd-9911-60c976c670fe" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_ed499a6a-f64b-4a90-9c5e-c7c6030f2e85" xlink:to="loc_srt_ConsolidationItemsDomain_45f62cdf-afd8-43bd-9911-60c976c670fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_6e4d9ab1-2fa7-4bbc-95bf-be4ce7be4ef5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_45f62cdf-afd8-43bd-9911-60c976c670fe" xlink:to="loc_us-gaap_OperatingSegmentsMember_6e4d9ab1-2fa7-4bbc-95bf-be4ce7be4ef5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_4c020ef9-2eb7-469d-b4f1-990f4694f116" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_45f62cdf-afd8-43bd-9911-60c976c670fe" xlink:to="loc_us-gaap_CorporateNonSegmentMember_4c020ef9-2eb7-469d-b4f1-990f4694f116" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_4148bc97-5321-4116-8f32-f5cb94ef4ada" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_a461176c-ac4f-456c-9a5f-00935990937d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_4148bc97-5321-4116-8f32-f5cb94ef4ada" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4148bc97-5321-4116-8f32-f5cb94ef4ada_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4148bc97-5321-4116-8f32-f5cb94ef4ada" xlink:to="loc_us-gaap_SegmentDomain_4148bc97-5321-4116-8f32-f5cb94ef4ada_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_c27bb42a-b13d-47da-838e-8863d7d6069b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4148bc97-5321-4116-8f32-f5cb94ef4ada" xlink:to="loc_us-gaap_SegmentDomain_c27bb42a-b13d-47da-838e-8863d7d6069b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsSegmentMember_3bd6bdf9-1a00-42dc-8774-32ab7e9d6971" xlink:href="dco-20221231.xsd#dco_ElectronicSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c27bb42a-b13d-47da-838e-8863d7d6069b" xlink:to="loc_dco_ElectronicSystemsSegmentMember_3bd6bdf9-1a00-42dc-8774-32ab7e9d6971" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsSegmentMember_ab665738-74ed-4f8f-aca9-a51a232a37f1" xlink:href="dco-20221231.xsd#dco_StructuralSystemsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c27bb42a-b13d-47da-838e-8863d7d6069b" xlink:to="loc_dco_StructuralSystemsSegmentMember_ab665738-74ed-4f8f-aca9-a51a232a37f1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/ConsolidatedValuationandQualifyingAccountsDetails" xlink:type="simple" xlink:href="dco-20221231.xsd#ConsolidatedValuationandQualifyingAccountsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/ConsolidatedValuationandQualifyingAccountsDetails" xlink:type="extended" id="iab960339b2914471905d9d424af8b1ad_ConsolidatedValuationandQualifyingAccountsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_7c1895ac-6942-4826-8f9b-380deba48a91" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ValuationAndQualifyingAccountsDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_b3edc665-2593-41d2-a0cb-ea4890a0e4c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MovementInValuationAllowancesAndReservesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_7c1895ac-6942-4826-8f9b-380deba48a91" xlink:to="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_b3edc665-2593-41d2-a0cb-ea4890a0e4c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_5cddfeae-8cbc-4e0f-ab5f-4ea25687e4b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_b3edc665-2593-41d2-a0cb-ea4890a0e4c2" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesBalance_5cddfeae-8cbc-4e0f-ab5f-4ea25687e4b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_e9a8878e-a679-4193-944d-90c12a833223" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_b3edc665-2593-41d2-a0cb-ea4890a0e4c2" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_e9a8878e-a679-4193-944d-90c12a833223" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDeductions_bcd27f77-8b22-4750-8efd-bc68532353fb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesDeductions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_b3edc665-2593-41d2-a0cb-ea4890a0e4c2" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDeductions_bcd27f77-8b22-4750-8efd-bc68532353fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesRecoveries_9a74343e-5d65-43de-b564-9c39f55e6313" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesRecoveries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_b3edc665-2593-41d2-a0cb-ea4890a0e4c2" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesRecoveries_9a74343e-5d65-43de-b564-9c39f55e6313" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesReservesOfBusinessesAcquired_8e31ae51-7320-4f04-a135-95d7f2c47956" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesReservesOfBusinessesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_b3edc665-2593-41d2-a0cb-ea4890a0e4c2" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesReservesOfBusinessesAcquired_8e31ae51-7320-4f04-a135-95d7f2c47956" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_d10f9e83-a986-4891-9a50-b2ba3a58685c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesBalance"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_a65d1b59-ca15-4d2f-9c3b-03ec4c7d1ff7" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ValuationAndQualifyingAccountsDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_7c1895ac-6942-4826-8f9b-380deba48a91" xlink:to="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_a65d1b59-ca15-4d2f-9c3b-03ec4c7d1ff7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_b5c6933e-117b-43f6-92cb-56406a5ebf44" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_a65d1b59-ca15-4d2f-9c3b-03ec4c7d1ff7" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_b5c6933e-117b-43f6-92cb-56406a5ebf44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_b5c6933e-117b-43f6-92cb-56406a5ebf44_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_b5c6933e-117b-43f6-92cb-56406a5ebf44" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_b5c6933e-117b-43f6-92cb-56406a5ebf44_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_10e947f5-4045-4d61-9cf6-a7d1d37596a2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowancesAndReservesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_b5c6933e-117b-43f6-92cb-56406a5ebf44" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_10e947f5-4045-4d61-9cf6-a7d1d37596a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForCreditLossMember_1c919587-92c7-4ae1-9094-b02ea6e67321" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllowanceForCreditLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_10e947f5-4045-4d61-9cf6-a7d1d37596a2" xlink:to="loc_us-gaap_AllowanceForCreditLossMember_1c919587-92c7-4ae1-9094-b02ea6e67321" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember_ba559217-94ee-4b75-bbd1-c6012643c922" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_10e947f5-4045-4d61-9cf6-a7d1d37596a2" xlink:to="loc_us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember_ba559217-94ee-4b75-bbd1-c6012643c922" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-roles-2022.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_OtherLiabilitiesCurrentAndNoncurrentMember_ac135fe3-4973-494e-8b35-f9d98b81797f" xlink:href="dco-20221231.xsd#dco_OtherLiabilitiesCurrentAndNoncurrentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract" xlink:to="loc_dco_OtherLiabilitiesCurrentAndNoncurrentMember_ac135fe3-4973-494e-8b35-f9d98b81797f" xlink:type="arc" order="1"/>
  </link:definitionLink>
</link:linkbase>
