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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2023 Workiva-->
<!--r:b462d94b-2c81-48ee-95ca-b5a85d8e3a9a,g:0d2c7373-f013-44fe-8d30-2949e4b68c89-->
<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/CondensedConsolidatedStatementsofChangesinShareholdersEquity" xlink:type="simple" xlink:href="dco-20230701.xsd#CondensedConsolidatedStatementsofChangesinShareholdersEquity"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/CondensedConsolidatedStatementsofChangesinShareholdersEquity" xlink:type="extended" id="i3c66924549d846fbaba875ab3cef785d_CondensedConsolidatedStatementsofChangesinShareholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_d715e92a-3fe8-441f-821a-6410e2cefbec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d715e92a-3fe8-441f-821a-6410e2cefbec" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_d9287309-c7e3-4a92-b2c3-0d7e761e0484" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_d9287309-c7e3-4a92-b2c3-0d7e761e0484" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_40414ae7-273d-4ee4-b286-f66bf0c135b5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockholdersEquity_40414ae7-273d-4ee4-b286-f66bf0c135b5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_db95b33e-4e21-4924-8241-ed6d545b3859" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_NetIncomeLoss_db95b33e-4e21-4924-8241-ed6d545b3859" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_a1069b26-28f4-43bf-a125-c068e29d1cbe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_a1069b26-28f4-43bf-a125-c068e29d1cbe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_8b2d6956-e473-4916-b336-0cf3304e1f52" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_8b2d6956-e473-4916-b336-0cf3304e1f52" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_40aaf19c-a92f-4f82-a025-b6d099a96728" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_40aaf19c-a92f-4f82-a025-b6d099a96728" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_d30d69c7-fa87-464b-aee8-470f8d72fa63" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_d30d69c7-fa87-464b-aee8-470f8d72fa63" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_bb461820-b7b5-4fc2-917d-b4d6feb8484a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_bb461820-b7b5-4fc2-917d-b4d6feb8484a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_64cdfb28-6bf8-4ceb-9dca-1d0b3de689ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_64cdfb28-6bf8-4ceb-9dca-1d0b3de689ba" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_b92c6c52-7bdf-41b0-afcf-2e3374b4eb78" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_b92c6c52-7bdf-41b0-afcf-2e3374b4eb78" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_3385318f-cc3d-486a-bd61-3e15a82550de" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_3385318f-cc3d-486a-bd61-3e15a82550de" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_acfa0f6b-7737-4537-ad17-3de0b477450e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_acfa0f6b-7737-4537-ad17-3de0b477450e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_87dc8fa4-7fbf-4866-902e-230923fcdc7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_87dc8fa4-7fbf-4866-902e-230923fcdc7c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_be3405e9-6492-485b-86b6-cd585f53be77" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_be3405e9-6492-485b-86b6-cd585f53be77" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_0f412f88-b19d-4279-8751-ca55e49431a8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_842735f3-2884-4d04-bffa-2cd3e473fe39" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_0f412f88-b19d-4279-8751-ca55e49431a8" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_1000c4e0-8688-4d51-abec-2ebecaa36544" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_9d3a2738-a555-44c5-9efe-16a1e58a5803" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_5bddb77e-8f00-46cb-97cd-f310e65c7a77" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_d715e92a-3fe8-441f-821a-6410e2cefbec" xlink:to="loc_us-gaap_StatementTable_5bddb77e-8f00-46cb-97cd-f310e65c7a77" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_95862926-b4cf-49f7-9787-d601e08be871" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_5bddb77e-8f00-46cb-97cd-f310e65c7a77" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_95862926-b4cf-49f7-9787-d601e08be871" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_95862926-b4cf-49f7-9787-d601e08be871_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_95862926-b4cf-49f7-9787-d601e08be871" xlink:to="loc_us-gaap_EquityComponentDomain_95862926-b4cf-49f7-9787-d601e08be871_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_808c4804-d33e-45d2-a3c6-38d752bf2431" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_95862926-b4cf-49f7-9787-d601e08be871" xlink:to="loc_us-gaap_EquityComponentDomain_808c4804-d33e-45d2-a3c6-38d752bf2431" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_5808bbbf-043f-4e68-8def-f44c6229aad4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_808c4804-d33e-45d2-a3c6-38d752bf2431" xlink:to="loc_us-gaap_CommonStockMember_5808bbbf-043f-4e68-8def-f44c6229aad4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_16af64a8-7019-4219-8393-60ec75fa3545" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_808c4804-d33e-45d2-a3c6-38d752bf2431" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_16af64a8-7019-4219-8393-60ec75fa3545" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_51ea0a52-5b89-4f9a-b873-21951ad90cb6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_808c4804-d33e-45d2-a3c6-38d752bf2431" xlink:to="loc_us-gaap_RetainedEarningsMember_51ea0a52-5b89-4f9a-b873-21951ad90cb6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_396690fb-bc4b-44c9-9b76-7295a751cec2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_808c4804-d33e-45d2-a3c6-38d752bf2431" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_396690fb-bc4b-44c9-9b76-7295a751cec2" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended" id="ib73a78fd4bc540e0912b89ad6e979d76_SummaryofSignificantAccountingPoliciesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:href="dco-20230701.xsd#dco_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_7f1b7547-e298-4906-b2a6-b5310058b638" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_NumberOfReportableSegments_7f1b7547-e298-4906-b2a6-b5310058b638" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_5b076488-36f0-49fd-8ad7-11fc0ae39576" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_DerivativeNotionalAmount_5b076488-36f0-49fd-8ad7-11fc0ae39576" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_c66fbe82-58e7-4010-8d0c-123a0f1ee56c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_c66fbe82-58e7-4010-8d0c-123a0f1ee56c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_5fa2fc5d-a95f-4717-bf71-f4a2b6804268" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_5fa2fc5d-a95f-4717-bf71-f4a2b6804268" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProductionCostOfContractsCurrent_9efb8e06-dd50-49f0-9f8f-593fa389f19e" xlink:href="dco-20230701.xsd#dco_ProductionCostOfContractsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_ProductionCostOfContractsCurrent_9efb8e06-dd50-49f0-9f8f-593fa389f19e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_8e4282ea-fd51-4e64-b77d-e55adffc4334" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_8e4282ea-fd51-4e64-b77d-e55adffc4334" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_5f57b700-0eb4-4528-99e6-0cf2ad4bfd67" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_5f57b700-0eb4-4528-99e6-0cf2ad4bfd67" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_cc6fe0fe-d7ba-4925-bcd3-2e6e0cac606d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_cc6fe0fe-d7ba-4925-bcd3-2e6e0cac606d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8e9b4258-1a45-4a1f-9b37-5e5b7365f881" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8e9b4258-1a45-4a1f-9b37-5e5b7365f881" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantsReceivable_0027c9a3-3b8f-4505-9199-9e176e3dec9d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GrantsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_GrantsReceivable_0027c9a3-3b8f-4505-9199-9e176e3dec9d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProceedsReceivedFromGrants_cb6348ae-f3bd-4e72-9f3f-cdc42a1f2430" xlink:href="dco-20230701.xsd#dco_ProceedsReceivedFromGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_ProceedsReceivedFromGrants_cb6348ae-f3bd-4e72-9f3f-cdc42a1f2430" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GovernmentGrantExpense_cbfa7dec-2b41-4a21-bcb8-099e71e07578" xlink:href="dco-20230701.xsd#dco_GovernmentGrantExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_GovernmentGrantExpense_cbfa7dec-2b41-4a21-bcb8-099e71e07578" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:href="dco-20230701.xsd#dco_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_b1785e84-125d-4efd-83b0-a9ae7298a171" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_b1785e84-125d-4efd-83b0-a9ae7298a171" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_6397180e-8ffa-4f2f-9fbd-4d42b967c37a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_6397180e-8ffa-4f2f-9fbd-4d42b967c37a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_97434eac-c9c8-473b-8bcc-e421775b043c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_97434eac-c9c8-473b-8bcc-e421775b043c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_2280d092-86de-4d6f-983c-82ae3397a3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_97434eac-c9c8-473b-8bcc-e421775b043c" xlink:to="loc_us-gaap_InterestRateSwapMember_2280d092-86de-4d6f-983c-82ae3397a3f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_2de0d6f4-123d-4976-9ebd-65226abe1da8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_2de0d6f4-123d-4976-9ebd-65226abe1da8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_2ad37ef8-72d2-462a-8431-f36013a7a614" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:to="loc_us-gaap_CostOfSalesMember_2ad37ef8-72d2-462a-8431-f36013a7a614" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_e5c59a17-fba3-4dd5-8ae7-1f82eb77f5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_e5c59a17-fba3-4dd5-8ae7-1f82eb77f5c2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails_1" xlink:type="simple" xlink:href="dco-20230701.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails_1" xlink:type="extended" id="i166f20d585d94a8aa2445cdffd44cd08_SummaryofSignificantAccountingPoliciesNarrativeDetails_1">
    <link:loc xlink:type="locator" xlink:label="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:href="dco-20230701.xsd#dco_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_7f1b7547-e298-4906-b2a6-b5310058b638" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_NumberOfReportableSegments_7f1b7547-e298-4906-b2a6-b5310058b638" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_5b076488-36f0-49fd-8ad7-11fc0ae39576" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_DerivativeNotionalAmount_5b076488-36f0-49fd-8ad7-11fc0ae39576" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_c66fbe82-58e7-4010-8d0c-123a0f1ee56c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_c66fbe82-58e7-4010-8d0c-123a0f1ee56c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_5fa2fc5d-a95f-4717-bf71-f4a2b6804268" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_5fa2fc5d-a95f-4717-bf71-f4a2b6804268" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProductionCostOfContractsCurrent_9efb8e06-dd50-49f0-9f8f-593fa389f19e" xlink:href="dco-20230701.xsd#dco_ProductionCostOfContractsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_ProductionCostOfContractsCurrent_9efb8e06-dd50-49f0-9f8f-593fa389f19e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_8e4282ea-fd51-4e64-b77d-e55adffc4334" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_8e4282ea-fd51-4e64-b77d-e55adffc4334" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_5f57b700-0eb4-4528-99e6-0cf2ad4bfd67" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_5f57b700-0eb4-4528-99e6-0cf2ad4bfd67" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_cc6fe0fe-d7ba-4925-bcd3-2e6e0cac606d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_cc6fe0fe-d7ba-4925-bcd3-2e6e0cac606d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8e9b4258-1a45-4a1f-9b37-5e5b7365f881" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_8e9b4258-1a45-4a1f-9b37-5e5b7365f881" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrantsReceivable_0027c9a3-3b8f-4505-9199-9e176e3dec9d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GrantsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_us-gaap_GrantsReceivable_0027c9a3-3b8f-4505-9199-9e176e3dec9d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProceedsReceivedFromGrants_cb6348ae-f3bd-4e72-9f3f-cdc42a1f2430" xlink:href="dco-20230701.xsd#dco_ProceedsReceivedFromGrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_ProceedsReceivedFromGrants_cb6348ae-f3bd-4e72-9f3f-cdc42a1f2430" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GovernmentGrantExpense_cbfa7dec-2b41-4a21-bcb8-099e71e07578" xlink:href="dco-20230701.xsd#dco_GovernmentGrantExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_GovernmentGrantExpense_cbfa7dec-2b41-4a21-bcb8-099e71e07578" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:href="dco-20230701.xsd#dco_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dco_SignificantAccountingPoliciesLineItems_1bc50fcd-03e9-432a-bb48-6638fde40eef" xlink:to="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_6397180e-8ffa-4f2f-9fbd-4d42b967c37a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_6397180e-8ffa-4f2f-9fbd-4d42b967c37a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_97434eac-c9c8-473b-8bcc-e421775b043c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_6397180e-8ffa-4f2f-9fbd-4d42b967c37a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_97434eac-c9c8-473b-8bcc-e421775b043c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_2280d092-86de-4d6f-983c-82ae3397a3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_97434eac-c9c8-473b-8bcc-e421775b043c" xlink:to="loc_us-gaap_InterestRateSwapMember_2280d092-86de-4d6f-983c-82ae3397a3f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dco_SignificantAccountingPoliciesTable_96e97ab2-b4e5-4298-9d7c-09773f31242c" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_2de0d6f4-123d-4976-9ebd-65226abe1da8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_2de0d6f4-123d-4976-9ebd-65226abe1da8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_2de0d6f4-123d-4976-9ebd-65226abe1da8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_2ad37ef8-72d2-462a-8431-f36013a7a614" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:to="loc_us-gaap_CostOfSalesMember_2ad37ef8-72d2-462a-8431-f36013a7a614" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_e5c59a17-fba3-4dd5-8ae7-1f82eb77f5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_f82946a7-7a13-4a67-9ed1-ca114a51c277" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_e5c59a17-fba3-4dd5-8ae7-1f82eb77f5c2" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails" xlink:type="extended" id="i5578adaee4ce4fdfb662a55f21cd14a5_SummaryofSignificantAccountingPoliciesWeightedAverageNumberofSharesOutstandingExcludedfromComputationofDilutedEarningsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_75ec1a3a-41b8-4eda-8c73-78d45138e08e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_7faeb38e-787e-4e72-8869-b7ddcfcb8335" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_75ec1a3a-41b8-4eda-8c73-78d45138e08e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_7faeb38e-787e-4e72-8869-b7ddcfcb8335" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_42db8db2-80a9-49f8-ae9e-5e24b34ac9a8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_75ec1a3a-41b8-4eda-8c73-78d45138e08e" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_42db8db2-80a9-49f8-ae9e-5e24b34ac9a8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_13f52a33-59c3-49de-9faf-6afa1de0b060" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_42db8db2-80a9-49f8-ae9e-5e24b34ac9a8" xlink:to="loc_us-gaap_AwardTypeAxis_13f52a33-59c3-49de-9faf-6afa1de0b060" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13f52a33-59c3-49de-9faf-6afa1de0b060_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_13f52a33-59c3-49de-9faf-6afa1de0b060" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_13f52a33-59c3-49de-9faf-6afa1de0b060_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3b30af74-b419-4fe9-bf69-3d694bb09d20" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_13f52a33-59c3-49de-9faf-6afa1de0b060" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3b30af74-b419-4fe9-bf69-3d694bb09d20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StockOptionsAndRestrictedStockUnitsMember_01c06bf8-8a83-4fc1-9e37-88b5ec2e09ad" xlink:href="dco-20230701.xsd#dco_StockOptionsAndRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3b30af74-b419-4fe9-bf69-3d694bb09d20" xlink:to="loc_dco_StockOptionsAndRestrictedStockUnitsMember_01c06bf8-8a83-4fc1-9e37-88b5ec2e09ad" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails" xlink:type="extended" id="ia5d83b42b55a4212bc1d3a8c0f9d9692_SummaryofSignificantAccountingPoliciesDisaggregatedRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_9094cf09-e2ca-4db6-83b0-2a1e4552e834" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_688fe8f1-7fee-4b0e-86f0-81c2cf595478" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_9094cf09-e2ca-4db6-83b0-2a1e4552e834" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_688fe8f1-7fee-4b0e-86f0-81c2cf595478" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_ed81a783-f257-431a-aabd-db22950256f7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_9094cf09-e2ca-4db6-83b0-2a1e4552e834" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_ed81a783-f257-431a-aabd-db22950256f7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_f4ec53c6-e396-4310-891f-dab43457571a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ed81a783-f257-431a-aabd-db22950256f7" xlink:to="loc_srt_ProductOrServiceAxis_f4ec53c6-e396-4310-891f-dab43457571a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_f4ec53c6-e396-4310-891f-dab43457571a_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_f4ec53c6-e396-4310-891f-dab43457571a" xlink:to="loc_srt_ProductsAndServicesDomain_f4ec53c6-e396-4310-891f-dab43457571a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_fadea3e4-412c-4127-a7fe-c1cfdc2e07d3" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_f4ec53c6-e396-4310-891f-dab43457571a" xlink:to="loc_srt_ProductsAndServicesDomain_fadea3e4-412c-4127-a7fe-c1cfdc2e07d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MilitaryandSpaceMember_b4e1a080-22d3-4ffa-b083-7597df232e46" xlink:href="dco-20230701.xsd#dco_MilitaryandSpaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_fadea3e4-412c-4127-a7fe-c1cfdc2e07d3" xlink:to="loc_dco_MilitaryandSpaceMember_b4e1a080-22d3-4ffa-b083-7597df232e46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_CommercialAerospaceMember_82697027-d5da-411e-991d-6de138b20c50" xlink:href="dco-20230701.xsd#dco_CommercialAerospaceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_fadea3e4-412c-4127-a7fe-c1cfdc2e07d3" xlink:to="loc_dco_CommercialAerospaceMember_82697027-d5da-411e-991d-6de138b20c50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_IndustrialMember_8a275b00-4072-4c0b-a992-de4990a326a5" xlink:href="dco-20230701.xsd#dco_IndustrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_fadea3e4-412c-4127-a7fe-c1cfdc2e07d3" xlink:to="loc_dco_IndustrialMember_8a275b00-4072-4c0b-a992-de4990a326a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_2e6ba9b6-ad99-418d-a191-fa7e17610817" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ed81a783-f257-431a-aabd-db22950256f7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_2e6ba9b6-ad99-418d-a191-fa7e17610817" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_2e6ba9b6-ad99-418d-a191-fa7e17610817_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2e6ba9b6-ad99-418d-a191-fa7e17610817" xlink:to="loc_us-gaap_SegmentDomain_2e6ba9b6-ad99-418d-a191-fa7e17610817_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8b4d75ba-96c0-40c7-8c52-27a74c5d73f0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_2e6ba9b6-ad99-418d-a191-fa7e17610817" xlink:to="loc_us-gaap_SegmentDomain_8b4d75ba-96c0-40c7-8c52-27a74c5d73f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsMember_3518ee6f-4a23-4642-b8c1-c2132d0fdcaf" xlink:href="dco-20230701.xsd#dco_ElectronicSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8b4d75ba-96c0-40c7-8c52-27a74c5d73f0" xlink:to="loc_dco_ElectronicSystemsMember_3518ee6f-4a23-4642-b8c1-c2132d0fdcaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsMember_9a0aeaef-0a57-48ec-ad56-1e9f259d3dc1" xlink:href="dco-20230701.xsd#dco_StructuralSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8b4d75ba-96c0-40c7-8c52-27a74c5d73f0" xlink:to="loc_dco_StructuralSystemsMember_9a0aeaef-0a57-48ec-ad56-1e9f259d3dc1" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessCombinationsNarrativeDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#BusinessCombinationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessCombinationsNarrativeDetails" xlink:type="extended" id="i75c182ee27fc4f0596704a90f0edb957_BusinessCombinationsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_0c6c7abd-7fee-4eaa-bce8-8f1609bab029" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_0c6c7abd-7fee-4eaa-bce8-8f1609bab029" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_080e3e7b-a1d3-41a8-833c-ff4afd81b23e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_080e3e7b-a1d3-41a8-833c-ff4afd81b23e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_e305d0b1-e10b-473c-b7a0-12fa4636bc88" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_e305d0b1-e10b-473c-b7a0-12fa4636bc88" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_2bf70459-ae7f-4874-a5e6-30b79fc82db1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_2bf70459-ae7f-4874-a5e6-30b79fc82db1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_de306937-ff1a-44c2-8815-737e03bcaba4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_Goodwill_de306937-ff1a-44c2-8815-737e03bcaba4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_b7b51de8-fef2-436e-9a93-151fb868c80f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_b7b51de8-fef2-436e-9a93-151fb868c80f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_04700578-fecb-4078-8d8a-d978caf702a7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAcquiredFromAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_04700578-fecb-4078-8d8a-d978caf702a7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_ae3d3b0b-0f32-40d8-a310-fa01dc6c2ffc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_ae3d3b0b-0f32-40d8-a310-fa01dc6c2ffc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_c6023adf-df62-4824-b4d6-5192815d470d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_c6023adf-df62-4824-b4d6-5192815d470d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_056ff11c-75c0-4930-b920-dea99e1467fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_056ff11c-75c0-4930-b920-dea99e1467fd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_cfb06e06-3588-434e-83a2-897ffbd54165" xlink:href="dco-20230701.xsd#dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_cfb06e06-3588-434e-83a2-897ffbd54165" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_e4559336-f16c-43da-ab42-347ceb375591" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_e4559336-f16c-43da-ab42-347ceb375591" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_dfa138ad-d48f-4819-a56d-279c3a21b6b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_dfa138ad-d48f-4819-a56d-279c3a21b6b3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_e56c9302-c1ac-4c84-9f3f-f416dcec5226" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_e56c9302-c1ac-4c84-9f3f-f416dcec5226" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_c067d7ea-14f1-4063-b28e-1241a99ae409" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_c067d7ea-14f1-4063-b28e-1241a99ae409" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_b2cabaf7-06c1-401f-aaa1-4a5532075c2f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIndefiniteLivedIntangibleAssets_b2cabaf7-06c1-401f-aaa1-4a5532075c2f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_4ad93273-2c39-440e-8020-d600aa6f3700" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_4ad93273-2c39-440e-8020-d600aa6f3700" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a33e73c9-157d-4382-be93-e9db3dc9151b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_422b7109-f6dd-4586-847f-8bf9dff1e4bc" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a33e73c9-157d-4382-be93-e9db3dc9151b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_4c8d3a0d-d7e2-45cc-a8c2-c43230ba6b5d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a33e73c9-157d-4382-be93-e9db3dc9151b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_4c8d3a0d-d7e2-45cc-a8c2-c43230ba6b5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4c8d3a0d-d7e2-45cc-a8c2-c43230ba6b5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_4c8d3a0d-d7e2-45cc-a8c2-c43230ba6b5d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4c8d3a0d-d7e2-45cc-a8c2-c43230ba6b5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b01b5e2f-8658-4b47-9f9c-86247d6b7bf9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_4c8d3a0d-d7e2-45cc-a8c2-c43230ba6b5d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b01b5e2f-8658-4b47-9f9c-86247d6b7bf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BLRAerospaceLLCMember_5b1c9cbb-6bf9-48a4-b478-c5bba2cfb82a" xlink:href="dco-20230701.xsd#dco_BLRAerospaceLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b01b5e2f-8658-4b47-9f9c-86247d6b7bf9" xlink:to="loc_dco_BLRAerospaceLLCMember_5b1c9cbb-6bf9-48a4-b478-c5bba2cfb82a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_MagneticSealCorporationMember_30702db1-ae12-49e5-ab56-f8b875e485b8" xlink:href="dco-20230701.xsd#dco_MagneticSealCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b01b5e2f-8658-4b47-9f9c-86247d6b7bf9" xlink:to="loc_dco_MagneticSealCorporationMember_30702db1-ae12-49e5-ab56-f8b875e485b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_d49857b6-52d1-43d6-9169-83e04b64b279" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a33e73c9-157d-4382-be93-e9db3dc9151b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_d49857b6-52d1-43d6-9169-83e04b64b279" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d49857b6-52d1-43d6-9169-83e04b64b279_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_d49857b6-52d1-43d6-9169-83e04b64b279" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d49857b6-52d1-43d6-9169-83e04b64b279_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f709cb53-513b-46c8-8f25-359cd624d716" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_d49857b6-52d1-43d6-9169-83e04b64b279" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f709cb53-513b-46c8-8f25-359cd624d716" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_9eee9134-fcd1-42a0-844d-f71f074ebed1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f709cb53-513b-46c8-8f25-359cd624d716" xlink:to="loc_us-gaap_CustomerRelationshipsMember_9eee9134-fcd1-42a0-844d-f71f074ebed1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OrderOrProductionBacklogMember_ffca3e4f-23f4-429d-a13a-b32c65d9d413" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OrderOrProductionBacklogMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f709cb53-513b-46c8-8f25-359cd624d716" xlink:to="loc_us-gaap_OrderOrProductionBacklogMember_ffca3e4f-23f4-429d-a13a-b32c65d9d413" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01ca5fe4-caf4-4653-a81c-4854be1be825" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_a33e73c9-157d-4382-be93-e9db3dc9151b" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01ca5fe4-caf4-4653-a81c-4854be1be825" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01ca5fe4-caf4-4653-a81c-4854be1be825_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01ca5fe4-caf4-4653-a81c-4854be1be825" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01ca5fe4-caf4-4653-a81c-4854be1be825_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_85b1cbe3-71ad-4746-9f32-a6818e4a5a96" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01ca5fe4-caf4-4653-a81c-4854be1be825" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_85b1cbe3-71ad-4746-9f32-a6818e4a5a96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_3a858fa8-8622-4f9f-b330-538b935b5280" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_85b1cbe3-71ad-4746-9f32-a6818e4a5a96" xlink:to="loc_us-gaap_TradeNamesMember_3a858fa8-8622-4f9f-b330-538b935b5280" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails" xlink:type="extended" id="ifa1dc2d16716452fb0b3c13a42ee8337_BusinessCombinationsFairValueofAssetsandLiabilitiesAcquiredDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_d63a71e7-1572-4b4a-a9f9-43c84989ac1b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_d63a71e7-1572-4b4a-a9f9-43c84989ac1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_634c45a2-a6f2-4704-9a27-2c2f8fe620f8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_634c45a2-a6f2-4704-9a27-2c2f8fe620f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_68b907e2-fc97-4daf-8a69-0630ab31acdd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_68b907e2-fc97-4daf-8a69-0630ab31acdd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_9eba725f-f52f-4248-84a0-27e0df959ae1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_9eba725f-f52f-4248-84a0-27e0df959ae1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_50cb97fb-1541-4bc1-8f5e-39bb61932d02" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_50cb97fb-1541-4bc1-8f5e-39bb61932d02" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_3a464a38-a696-4998-bb81-df4a076b6ad4" xlink:href="dco-20230701.xsd#dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAssets_3a464a38-a696-4998-bb81-df4a076b6ad4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_5c4dc2aa-e970-4e16-981f-bfa99033d8cb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_5c4dc2aa-e970-4e16-981f-bfa99033d8cb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_46026a8e-b74b-499f-963b-c23cf7375871" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_Goodwill_46026a8e-b74b-499f-963b-c23cf7375871" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedAssets_de4db743-e351-4834-9837-9f2e6a7da573" xlink:href="dco-20230701.xsd#dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_dco_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedAssets_de4db743-e351-4834-9837-9f2e6a7da573" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_c79fdd7a-04f9-42bb-873d-e060ef63841b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_c79fdd7a-04f9-42bb-873d-e060ef63841b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_71695c9f-243a-4bad-a10c-219d692086ca" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_71695c9f-243a-4bad-a10c-219d692086ca" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_cd943fd9-7794-4834-9c68-bcfb9cb30320" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_cd943fd9-7794-4834-9c68-bcfb9cb30320" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_72df40db-5f98-46b2-bb26-47966e06b69c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_72df40db-5f98-46b2-bb26-47966e06b69c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_30a059e8-129c-4c5d-937b-f1ff99c14a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_830f531c-222d-4da4-b888-700240de5219" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_30a059e8-129c-4c5d-937b-f1ff99c14a6f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_61641160-c72f-4ac3-bd76-3dc4da4ab465" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_30a059e8-129c-4c5d-937b-f1ff99c14a6f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_61641160-c72f-4ac3-bd76-3dc4da4ab465" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_61641160-c72f-4ac3-bd76-3dc4da4ab465_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_61641160-c72f-4ac3-bd76-3dc4da4ab465" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_61641160-c72f-4ac3-bd76-3dc4da4ab465_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_72605549-f136-443f-ba3e-cfc67ce42751" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_61641160-c72f-4ac3-bd76-3dc4da4ab465" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_72605549-f136-443f-ba3e-cfc67ce42751" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BLRAerospaceLLCMember_b0e14235-8bbc-420a-b4e9-f266b8dca672" xlink:href="dco-20230701.xsd#dco_BLRAerospaceLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_72605549-f136-443f-ba3e-cfc67ce42751" xlink:to="loc_dco_BLRAerospaceLLCMember_b0e14235-8bbc-420a-b4e9-f266b8dca672" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails" xlink:type="extended" id="i9df5c190a94e4013bc4e6d60e5880557_BusinessCombinationsEstimatedFairValueofIntangibleAssetsAcquiredDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_ff73686c-991b-430c-928c-dd95cec14945" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_1ce0d05c-5eed-4f86-974c-f4768ae64d15" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_ff73686c-991b-430c-928c-dd95cec14945" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_1ce0d05c-5eed-4f86-974c-f4768ae64d15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_e8fa56a6-afe3-4b13-a22c-b77e130bf584" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_ff73686c-991b-430c-928c-dd95cec14945" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_e8fa56a6-afe3-4b13-a22c-b77e130bf584" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_6a8da239-721d-4783-9164-679eaa3b28a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_ff73686c-991b-430c-928c-dd95cec14945" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_6a8da239-721d-4783-9164-679eaa3b28a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0e6fb056-7b25-450a-b165-f9808ef3db7e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_ff73686c-991b-430c-928c-dd95cec14945" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0e6fb056-7b25-450a-b165-f9808ef3db7e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_5a37d7ae-8c51-4115-9adb-2bcc30da813f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0e6fb056-7b25-450a-b165-f9808ef3db7e" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_5a37d7ae-8c51-4115-9adb-2bcc30da813f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5a37d7ae-8c51-4115-9adb-2bcc30da813f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5a37d7ae-8c51-4115-9adb-2bcc30da813f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5a37d7ae-8c51-4115-9adb-2bcc30da813f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cd38906a-2610-4ee0-8ab5-3645d519521d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5a37d7ae-8c51-4115-9adb-2bcc30da813f" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cd38906a-2610-4ee0-8ab5-3645d519521d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BLRAerospaceLLCMember_91d88c3d-7e0a-4d07-a7ef-f5686ea7654d" xlink:href="dco-20230701.xsd#dco_BLRAerospaceLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cd38906a-2610-4ee0-8ab5-3645d519521d" xlink:to="loc_dco_BLRAerospaceLLCMember_91d88c3d-7e0a-4d07-a7ef-f5686ea7654d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2d90a506-8792-4295-b726-8f6dc573dba0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0e6fb056-7b25-450a-b165-f9808ef3db7e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2d90a506-8792-4295-b726-8f6dc573dba0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2d90a506-8792-4295-b726-8f6dc573dba0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2d90a506-8792-4295-b726-8f6dc573dba0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2d90a506-8792-4295-b726-8f6dc573dba0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ffbae0b0-076d-45d3-b916-1c605b2ff5ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_2d90a506-8792-4295-b726-8f6dc573dba0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ffbae0b0-076d-45d3-b916-1c605b2ff5ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_a6e15294-4b7b-42c4-b31f-47ecc6288f2f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ffbae0b0-076d-45d3-b916-1c605b2ff5ea" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_a6e15294-4b7b-42c4-b31f-47ecc6288f2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_3bbe48ea-9e6d-4543-81ff-9243aa7f43f9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ffbae0b0-076d-45d3-b916-1c605b2ff5ea" xlink:to="loc_us-gaap_CustomerRelationshipsMember_3bbe48ea-9e6d-4543-81ff-9243aa7f43f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_2b7fcbdc-167d-4772-a7f2-8ef4b4f624e9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_ffbae0b0-076d-45d3-b916-1c605b2ff5ea" xlink:to="loc_us-gaap_TradeNamesMember_2b7fcbdc-167d-4772-a7f2-8ef4b4f624e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b78080e8-82da-4056-bea4-926888e1a824" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_0e6fb056-7b25-450a-b165-f9808ef3db7e" xlink:to="loc_srt_RangeAxis_b78080e8-82da-4056-bea4-926888e1a824" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b78080e8-82da-4056-bea4-926888e1a824_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b78080e8-82da-4056-bea4-926888e1a824" xlink:to="loc_srt_RangeMember_b78080e8-82da-4056-bea4-926888e1a824_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_457c8252-6192-4f47-80c0-845d61e4914e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b78080e8-82da-4056-bea4-926888e1a824" xlink:to="loc_srt_RangeMember_457c8252-6192-4f47-80c0-845d61e4914e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_4b508d3d-363c-4a99-bb71-5160a2680eae" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_457c8252-6192-4f47-80c0-845d61e4914e" xlink:to="loc_srt_MinimumMember_4b508d3d-363c-4a99-bb71-5160a2680eae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_0cc4b6c0-65ef-4bf1-9cb2-3b7696079fbe" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_457c8252-6192-4f47-80c0-845d61e4914e" xlink:to="loc_srt_MaximumMember_0cc4b6c0-65ef-4bf1-9cb2-3b7696079fbe" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/RestructuringActivitiesNarrativeDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#RestructuringActivitiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/RestructuringActivitiesNarrativeDetails" xlink:type="extended" id="i51f43545c33a4172b29f038e3fe58ce8_RestructuringActivitiesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_6fa042eb-81f0-4b86-83cc-eb4f19557d3a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:to="loc_us-gaap_RestructuringCharges_6fa042eb-81f0-4b86-83cc-eb4f19557d3a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_fb2047b0-cd3d-4dbc-87c5-64eac262fead" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringAndRelatedCostIncurredCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:to="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_fb2047b0-cd3d-4dbc-87c5-64eac262fead" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_229c4313-bafb-40a2-9f5a-86816fdf1a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_229c4313-bafb-40a2-9f5a-86816fdf1a7b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_55d58595-b51c-40f5-896c-88fb215b160a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringAndRelatedCostExpectedCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:to="loc_us-gaap_RestructuringAndRelatedCostExpectedCost1_55d58595-b51c-40f5-896c-88fb215b160a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringCosts_1106eba6-83a2-4333-af2c-2763656b16c4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherRestructuringCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:to="loc_us-gaap_OtherRestructuringCosts_1106eba6-83a2-4333-af2c-2763656b16c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_205ede6a-c098-43e2-8227-56275cc097ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:to="loc_us-gaap_RestructuringReserve_205ede6a-c098-43e2-8227-56275cc097ea" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_78bbeb8f-b633-47cd-b2d1-9e5767721b49" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_e4237e39-d9be-45f1-8a1d-25e345378f82" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_78bbeb8f-b633-47cd-b2d1-9e5767721b49" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e2d84603-1cb9-4291-8c5b-c243ec3b9e9e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_78bbeb8f-b633-47cd-b2d1-9e5767721b49" xlink:to="loc_srt_RangeAxis_e2d84603-1cb9-4291-8c5b-c243ec3b9e9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e2d84603-1cb9-4291-8c5b-c243ec3b9e9e_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e2d84603-1cb9-4291-8c5b-c243ec3b9e9e" xlink:to="loc_srt_RangeMember_e2d84603-1cb9-4291-8c5b-c243ec3b9e9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4770ed29-6912-4ef3-bfbd-61dcc66b7a86" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e2d84603-1cb9-4291-8c5b-c243ec3b9e9e" xlink:to="loc_srt_RangeMember_4770ed29-6912-4ef3-bfbd-61dcc66b7a86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_a94c188a-73c7-460c-ad9c-a4da3136c09e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4770ed29-6912-4ef3-bfbd-61dcc66b7a86" xlink:to="loc_srt_MinimumMember_a94c188a-73c7-460c-ad9c-a4da3136c09e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_9ffd04f4-02a4-4a2f-a37f-c401fc0affd4" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4770ed29-6912-4ef3-bfbd-61dcc66b7a86" xlink:to="loc_srt_MaximumMember_9ffd04f4-02a4-4a2f-a37f-c401fc0affd4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_cf94c74d-fa59-4e7e-a212-2f984c0e16e1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_78bbeb8f-b633-47cd-b2d1-9e5767721b49" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_cf94c74d-fa59-4e7e-a212-2f984c0e16e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_cf94c74d-fa59-4e7e-a212-2f984c0e16e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_cf94c74d-fa59-4e7e-a212-2f984c0e16e1" xlink:to="loc_us-gaap_SegmentDomain_cf94c74d-fa59-4e7e-a212-2f984c0e16e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_cf5aa986-6b5d-4269-860d-0560cb3bac3c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_cf94c74d-fa59-4e7e-a212-2f984c0e16e1" xlink:to="loc_us-gaap_SegmentDomain_cf5aa986-6b5d-4269-860d-0560cb3bac3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsMember_0ff29b4f-d84b-44e2-8746-ef5a9f7eee9a" xlink:href="dco-20230701.xsd#dco_ElectronicSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cf5aa986-6b5d-4269-860d-0560cb3bac3c" xlink:to="loc_dco_ElectronicSystemsMember_0ff29b4f-d84b-44e2-8746-ef5a9f7eee9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsMember_6dcc777a-67df-4541-bbe2-238c30e612a0" xlink:href="dco-20230701.xsd#dco_StructuralSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cf5aa986-6b5d-4269-860d-0560cb3bac3c" xlink:to="loc_dco_StructuralSystemsMember_6dcc777a-67df-4541-bbe2-238c30e612a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_4e4ad625-cdae-4dba-9782-b260fc0725c0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_78bbeb8f-b633-47cd-b2d1-9e5767721b49" xlink:to="loc_us-gaap_RestructuringPlanAxis_4e4ad625-cdae-4dba-9782-b260fc0725c0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_4e4ad625-cdae-4dba-9782-b260fc0725c0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_4e4ad625-cdae-4dba-9782-b260fc0725c0" xlink:to="loc_us-gaap_RestructuringPlanDomain_4e4ad625-cdae-4dba-9782-b260fc0725c0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_48059ef7-685e-4a96-8519-590632fd1ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_4e4ad625-cdae-4dba-9782-b260fc0725c0" xlink:to="loc_us-gaap_RestructuringPlanDomain_48059ef7-685e-4a96-8519-590632fd1ab2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_RestructuringPlan2022Member_c72ff3ba-31b2-4b64-9528-e40b3f346fa9" xlink:href="dco-20230701.xsd#dco_RestructuringPlan2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_48059ef7-685e-4a96-8519-590632fd1ab2" xlink:to="loc_dco_RestructuringPlan2022Member_c72ff3ba-31b2-4b64-9528-e40b3f346fa9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_0ff4f4c8-0142-40e4-8143-d87bafc37f11" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_78bbeb8f-b633-47cd-b2d1-9e5767721b49" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_0ff4f4c8-0142-40e4-8143-d87bafc37f11" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_0ff4f4c8-0142-40e4-8143-d87bafc37f11_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_0ff4f4c8-0142-40e4-8143-d87bafc37f11" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_0ff4f4c8-0142-40e4-8143-d87bafc37f11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_be14a554-6802-4c00-ad14-d44abc8d8c01" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_0ff4f4c8-0142-40e4-8143-d87bafc37f11" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_be14a554-6802-4c00-ad14-d44abc8d8c01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_40db0771-27f2-4e49-9dcc-ad844613b74e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_be14a554-6802-4c00-ad14-d44abc8d8c01" xlink:to="loc_us-gaap_EmployeeSeveranceMember_40db0771-27f2-4e49-9dcc-ad844613b74e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_d6d7b723-0b8f-4b7a-b3fd-d882c0bfcd63" xlink:href="dco-20230701.xsd#dco_PropertyAndEquipmentAcceleratedDepreciationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_be14a554-6802-4c00-ad14-d44abc8d8c01" xlink:to="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_d6d7b723-0b8f-4b7a-b3fd-d882c0bfcd63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyAndEquipmentImpairmentMember_d3fbca40-63de-41ff-8ed1-fe94e3c251fc" xlink:href="dco-20230701.xsd#dco_PropertyAndEquipmentImpairmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_be14a554-6802-4c00-ad14-d44abc8d8c01" xlink:to="loc_dco_PropertyAndEquipmentImpairmentMember_d3fbca40-63de-41ff-8ed1-fe94e3c251fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_InventoryWriteDownMember_325a02bb-3b0f-43eb-98cb-a7b49beb8192" xlink:href="dco-20230701.xsd#dco_InventoryWriteDownMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_be14a554-6802-4c00-ad14-d44abc8d8c01" xlink:to="loc_dco_InventoryWriteDownMember_325a02bb-3b0f-43eb-98cb-a7b49beb8192" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_baa82254-68d3-4997-875c-b010e0583b55" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_be14a554-6802-4c00-ad14-d44abc8d8c01" xlink:to="loc_us-gaap_OtherRestructuringMember_baa82254-68d3-4997-875c-b010e0583b55" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_da7492ec-4299-4a09-b8fc-c36d63c3afcb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_78bbeb8f-b633-47cd-b2d1-9e5767721b49" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_da7492ec-4299-4a09-b8fc-c36d63c3afcb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_da7492ec-4299-4a09-b8fc-c36d63c3afcb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_da7492ec-4299-4a09-b8fc-c36d63c3afcb" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_da7492ec-4299-4a09-b8fc-c36d63c3afcb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_9bd4029e-335a-4049-a4a3-349b598ffe49" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_da7492ec-4299-4a09-b8fc-c36d63c3afcb" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_9bd4029e-335a-4049-a4a3-349b598ffe49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_226b9a9d-b4f5-4ae2-a7eb-f8fa6fcc5f0a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_9bd4029e-335a-4049-a4a3-349b598ffe49" xlink:to="loc_us-gaap_CostOfSalesMember_226b9a9d-b4f5-4ae2-a7eb-f8fa6fcc5f0a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/RestructuringActivitiesOtherRestructuringActivitiesDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#RestructuringActivitiesOtherRestructuringActivitiesDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/RestructuringActivitiesOtherRestructuringActivitiesDetails" xlink:type="extended" id="i273e21780f914be0bf8bd2657144ee79_RestructuringActivitiesOtherRestructuringActivitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_cd60d10d-01b7-4170-b5f5-634bd730a52b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_d714870b-5fed-4a66-a192-a0602405cd5d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_cd60d10d-01b7-4170-b5f5-634bd730a52b" xlink:to="loc_us-gaap_RestructuringReserveRollForward_d714870b-5fed-4a66-a192-a0602405cd5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_3bb71719-870b-4454-8a11-fdfe680d8f62" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_d714870b-5fed-4a66-a192-a0602405cd5d" xlink:to="loc_us-gaap_RestructuringReserve_3bb71719-870b-4454-8a11-fdfe680d8f62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_758f2b91-b2a7-4484-ba4f-fb7239cdf26a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_d714870b-5fed-4a66-a192-a0602405cd5d" xlink:to="loc_us-gaap_RestructuringCharges_758f2b91-b2a7-4484-ba4f-fb7239cdf26a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_4b17cbc8-e3b8-414b-beb3-c012fe17c7ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_d714870b-5fed-4a66-a192-a0602405cd5d" xlink:to="loc_us-gaap_PaymentsForRestructuring_4b17cbc8-e3b8-414b-beb3-c012fe17c7ea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveSettledWithoutCash2_f8777296-7ab9-438a-8813-592d1478447e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserveSettledWithoutCash2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_d714870b-5fed-4a66-a192-a0602405cd5d" xlink:to="loc_us-gaap_RestructuringReserveSettledWithoutCash2_f8777296-7ab9-438a-8813-592d1478447e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAccrualAdjustment1_e5237bff-5f24-4971-9ed8-acb517c0555a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserveAccrualAdjustment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_d714870b-5fed-4a66-a192-a0602405cd5d" xlink:to="loc_us-gaap_RestructuringReserveAccrualAdjustment1_e5237bff-5f24-4971-9ed8-acb517c0555a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_4ac711c2-82b4-4fb5-85c0-75c945880a88" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserve"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_586945fa-d265-4c90-af68-d2dcae73a12f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_cd60d10d-01b7-4170-b5f5-634bd730a52b" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_586945fa-d265-4c90-af68-d2dcae73a12f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_e8ac579d-81e8-4b63-b738-ba4d9c25a790" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_586945fa-d265-4c90-af68-d2dcae73a12f" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_e8ac579d-81e8-4b63-b738-ba4d9c25a790" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_e8ac579d-81e8-4b63-b738-ba4d9c25a790_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_e8ac579d-81e8-4b63-b738-ba4d9c25a790" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_e8ac579d-81e8-4b63-b738-ba4d9c25a790_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_c358a32e-a929-4386-8f4b-9b52d642ede6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_e8ac579d-81e8-4b63-b738-ba4d9c25a790" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_c358a32e-a929-4386-8f4b-9b52d642ede6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_6a85d591-864b-4637-9dad-f1fa29d4c8f8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_c358a32e-a929-4386-8f4b-9b52d642ede6" xlink:to="loc_us-gaap_EmployeeSeveranceMember_6a85d591-864b-4637-9dad-f1fa29d4c8f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_c8e1f33a-81d4-48f2-bb7f-ecea12850e52" xlink:href="dco-20230701.xsd#dco_PropertyAndEquipmentAcceleratedDepreciationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_c358a32e-a929-4386-8f4b-9b52d642ede6" xlink:to="loc_dco_PropertyAndEquipmentAcceleratedDepreciationMember_c8e1f33a-81d4-48f2-bb7f-ecea12850e52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_06dec48a-85bb-4ab4-b8b7-ed8293ca6370" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_c358a32e-a929-4386-8f4b-9b52d642ede6" xlink:to="loc_us-gaap_OtherRestructuringMember_06dec48a-85bb-4ab4-b8b7-ed8293ca6370" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_a3b08a53-507e-43d4-babd-6acc498226cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_586945fa-d265-4c90-af68-d2dcae73a12f" xlink:to="loc_us-gaap_RestructuringPlanAxis_a3b08a53-507e-43d4-babd-6acc498226cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_a3b08a53-507e-43d4-babd-6acc498226cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_a3b08a53-507e-43d4-babd-6acc498226cc" xlink:to="loc_us-gaap_RestructuringPlanDomain_a3b08a53-507e-43d4-babd-6acc498226cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_8d6368fa-a557-4f54-a0e1-99d97b8e9870" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_a3b08a53-507e-43d4-babd-6acc498226cc" xlink:to="loc_us-gaap_RestructuringPlanDomain_8d6368fa-a557-4f54-a0e1-99d97b8e9870" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_RestructuringPlan2022Member_fc438a04-1dff-43f6-b339-114c6ea9d296" xlink:href="dco-20230701.xsd#dco_RestructuringPlan2022Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_8d6368fa-a557-4f54-a0e1-99d97b8e9870" xlink:to="loc_dco_RestructuringPlan2022Member_fc438a04-1dff-43f6-b339-114c6ea9d296" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/GoodwillDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#GoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/GoodwillDetails" xlink:type="extended" id="i00e6dc04879f4de3a5126caf80f8bd61_GoodwillDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_8bfc8640-55c6-4380-add1-ef3d266f56aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillGross_5179f9ec-9a6f-4c62-909f-657cbcc30fdd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GoodwillGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_8bfc8640-55c6-4380-add1-ef3d266f56aa" xlink:to="loc_us-gaap_GoodwillGross_5179f9ec-9a6f-4c62-909f-657cbcc30fdd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_cad17093-315d-41f1-a0fc-266dcccad13e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_8bfc8640-55c6-4380-add1-ef3d266f56aa" xlink:to="loc_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_cad17093-315d-41f1-a0fc-266dcccad13e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_2fdb0c09-2a47-4220-802d-ba0be44df71f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_8bfc8640-55c6-4380-add1-ef3d266f56aa" xlink:to="loc_us-gaap_Goodwill_2fdb0c09-2a47-4220-802d-ba0be44df71f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_096db3ff-b403-4ed1-80b0-3374eb827a10" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_8bfc8640-55c6-4380-add1-ef3d266f56aa" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_096db3ff-b403-4ed1-80b0-3374eb827a10" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_3a91a0b7-717f-4029-896a-727fad56f6ab" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_66a00245-ba07-428a-acaf-efcc0f359865" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_8bfc8640-55c6-4380-add1-ef3d266f56aa" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_66a00245-ba07-428a-acaf-efcc0f359865" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_fe41ab2b-4f6f-4b1d-aa81-96cacac88c65" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_66a00245-ba07-428a-acaf-efcc0f359865" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_fe41ab2b-4f6f-4b1d-aa81-96cacac88c65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_fe41ab2b-4f6f-4b1d-aa81-96cacac88c65_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_fe41ab2b-4f6f-4b1d-aa81-96cacac88c65" xlink:to="loc_us-gaap_SegmentDomain_fe41ab2b-4f6f-4b1d-aa81-96cacac88c65_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_0bb2a89f-0531-453e-a664-aeadaf55800a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_fe41ab2b-4f6f-4b1d-aa81-96cacac88c65" xlink:to="loc_us-gaap_SegmentDomain_0bb2a89f-0531-453e-a664-aeadaf55800a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsMember_523c2298-f628-4e7b-aaf8-8ef03a4ae9aa" xlink:href="dco-20230701.xsd#dco_ElectronicSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_0bb2a89f-0531-453e-a664-aeadaf55800a" xlink:to="loc_dco_ElectronicSystemsMember_523c2298-f628-4e7b-aaf8-8ef03a4ae9aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsMember_b90babad-66d0-4044-8cec-ab2f06db28ca" xlink:href="dco-20230701.xsd#dco_StructuralSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_0bb2a89f-0531-453e-a664-aeadaf55800a" xlink:to="loc_dco_StructuralSystemsMember_b90babad-66d0-4044-8cec-ab2f06db28ca" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/LongTermDebtScheduleofLongTermDebtDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#LongTermDebtScheduleofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/LongTermDebtScheduleofLongTermDebtDetails" xlink:type="extended" id="idbb0cd2d3cdb4726817904b6effc1862_LongTermDebtScheduleofLongTermDebtDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_f4321500-3234-4730-8789-cdff5f61f780" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_f4321500-3234-4730-8789-cdff5f61f780" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_566dbdd8-d37a-47e9-bdc6-7c52f080c414" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:to="loc_us-gaap_LongTermDebtCurrent_566dbdd8-d37a-47e9-bdc6-7c52f080c414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_0576295c-3e98-4dff-8a70-f298ed806f9c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_0576295c-3e98-4dff-8a70-f298ed806f9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_60cb5110-c55d-4440-9d00-9ed81abf7198" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_60cb5110-c55d-4440-9d00-9ed81abf7198" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_eb790f66-9b3b-487a-897e-d011d6afcbf7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:to="loc_us-gaap_LongTermDebt_eb790f66-9b3b-487a-897e-d011d6afcbf7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_3c84a1e4-967d-48c3-aa1b-6c36960f8c30" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_d0bf9d68-a442-4ac5-ad46-9a4ddedb437b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:to="loc_us-gaap_LongtermDebtWeightedAverageInterestRate_d0bf9d68-a442-4ac5-ad46-9a4ddedb437b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_83aa2113-85c5-43bb-8114-1c3a44314be2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_09cd8c44-1f60-4882-9765-456de3792f2c" xlink:to="loc_us-gaap_DebtInstrumentTable_83aa2113-85c5-43bb-8114-1c3a44314be2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_e384d9e0-c2bb-48a4-b111-0edfb5c7d085" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_83aa2113-85c5-43bb-8114-1c3a44314be2" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_e384d9e0-c2bb-48a4-b111-0edfb5c7d085" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e384d9e0-c2bb-48a4-b111-0edfb5c7d085_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e384d9e0-c2bb-48a4-b111-0edfb5c7d085" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e384d9e0-c2bb-48a4-b111-0edfb5c7d085_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_f0518c01-6d6a-4d81-a5a7-352043eeaccc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e384d9e0-c2bb-48a4-b111-0edfb5c7d085" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_f0518c01-6d6a-4d81-a5a7-352043eeaccc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SeniorSecuredTermLoanMember_20eadf95-6dcd-488f-acb1-6b71ee3ab0da" xlink:href="dco-20230701.xsd#dco_SeniorSecuredTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_f0518c01-6d6a-4d81-a5a7-352043eeaccc" xlink:to="loc_dco_SeniorSecuredTermLoanMember_20eadf95-6dcd-488f-acb1-6b71ee3ab0da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_e34d0d1b-e211-4d2a-ab41-597ebbea8ebc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_f0518c01-6d6a-4d81-a5a7-352043eeaccc" xlink:to="loc_us-gaap_LineOfCreditMember_e34d0d1b-e211-4d2a-ab41-597ebbea8ebc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/LongTermDebtNarrativeDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#LongTermDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/LongTermDebtNarrativeDetails" xlink:type="extended" id="ib3d9bb3ce8ff4ec4ad0067eecfa17b78_LongTermDebtNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_48e52039-a5cc-44a2-9546-52a30ccaa915" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_48e52039-a5cc-44a2-9546-52a30ccaa915" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_56cbe9ce-a588-4e93-8bda-30d97fd22f5d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_56cbe9ce-a588-4e93-8bda-30d97fd22f5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_c26ec35f-8699-4f1a-8e4b-ccb8530556ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_c26ec35f-8699-4f1a-8e4b-ccb8530556ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentBasisSpreadonFixedRateBaseRate_34d5aee9-7b96-47a7-a45a-fba95ed16273" xlink:href="dco-20230701.xsd#dco_DebtInstrumentBasisSpreadonFixedRateBaseRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_DebtInstrumentBasisSpreadonFixedRateBaseRate_34d5aee9-7b96-47a7-a45a-fba95ed16273" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPrepaymentAmountPercentageofPrincipalAmount_906a87dd-da1a-4e70-872e-31c3a154dfe6" xlink:href="dco-20230701.xsd#dco_DebtInstrumentPrepaymentAmountPercentageofPrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_DebtInstrumentPrepaymentAmountPercentageofPrincipalAmount_906a87dd-da1a-4e70-872e-31c3a154dfe6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfDebt_bf2c9aaa-a4de-4a6c-86e6-1f07cbef5828" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RepaymentsOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_RepaymentsOfDebt_bf2c9aaa-a4de-4a6c-86e6-1f07cbef5828" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_e2e7459e-6d89-415f-8142-52adb1e32203" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_e2e7459e-6d89-415f-8142-52adb1e32203" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisGreaterthan3.25_9de0a636-ea8f-4a15-857c-06fd3eb68fcc" xlink:href="dco-20230701.xsd#dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisGreaterthan3.25"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisGreaterthan3.25_9de0a636-ea8f-4a15-857c-06fd3eb68fcc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMinimum_11b2547a-7770-4f20-bedb-62acdd7d5ddd" xlink:href="dco-20230701.xsd#dco_DebtInstrumentCovenantAdjustedLeverageRatioMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMinimum_11b2547a-7770-4f20-bedb-62acdd7d5ddd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMaximum_02237a61-35a1-49a5-90fb-1c82377582fd" xlink:href="dco-20230701.xsd#dco_DebtInstrumentCovenantAdjustedLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_DebtInstrumentCovenantAdjustedLeverageRatioMaximum_02237a61-35a1-49a5-90fb-1c82377582fd" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPercentageOfExcessCashFlowPaymentWhenLeverageRatioIsLessThanOrEqualTo325ButGreaterThan250_d38cc874-2811-46c8-9fc4-ddc9e105684d" xlink:href="dco-20230701.xsd#dco_DebtInstrumentPercentageOfExcessCashFlowPaymentWhenLeverageRatioIsLessThanOrEqualTo325ButGreaterThan250"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_DebtInstrumentPercentageOfExcessCashFlowPaymentWhenLeverageRatioIsLessThanOrEqualTo325ButGreaterThan250_d38cc874-2811-46c8-9fc4-ddc9e105684d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessThanorEqualto2.50_840e0431-8245-4428-a3d6-cfaefb31e558" xlink:href="dco-20230701.xsd#dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessThanorEqualto2.50"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_DebtInstrumentPercentageofExcessCashFlowPaymentWhenLeverageRatioisLessThanorEqualto2.50_840e0431-8245-4428-a3d6-cfaefb31e558" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ProceedsFromTermLoan_1341f631-9390-4ffa-93af-3a39bd81fa95" xlink:href="dco-20230701.xsd#dco_ProceedsFromTermLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_ProceedsFromTermLoan_1341f631-9390-4ffa-93af-3a39bd81fa95" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_89de424d-26d6-42af-858d-6b2fa555688b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_LongTermDebt_89de424d-26d6-42af-858d-6b2fa555688b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_ed510923-9433-43d5-804c-b3ecb7c03e99" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_ed510923-9433-43d5-804c-b3ecb7c03e99" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfSecuredDebt_f4535533-3851-4244-b67e-1bb1ed0720ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RepaymentsOfSecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_RepaymentsOfSecuredDebt_f4535533-3851-4244-b67e-1bb1ed0720ec" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_f979dc8a-bdbf-4b9f-a6d1-25aea44e3389" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_f979dc8a-bdbf-4b9f-a6d1-25aea44e3389" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_9a4fe61b-b327-4894-8662-cce19ecb8dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredFinanceCostsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_9a4fe61b-b327-4894-8662-cce19ecb8dd5" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_3bf3e390-ee80-4724-8f05-f22fe8181fc2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_3bf3e390-ee80-4724-8f05-f22fe8181fc2" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_75ba302f-5cdd-4522-af65-71cc51d594bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_75ba302f-5cdd-4522-af65-71cc51d594bc" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_f245a351-04a6-40d7-91f8-ba27eec863dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_f245a351-04a6-40d7-91f8-ba27eec863dc" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_02ba4509-8ba9-4c40-ba61-d5346f0cdb30" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_02ba4509-8ba9-4c40-ba61-d5346f0cdb30" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NumberofSubsidiariesThatAreNotGuarantorsonDebt_46324147-6ede-4a01-a319-bb1438bc73c4" xlink:href="dco-20230701.xsd#dco_NumberofSubsidiariesThatAreNotGuarantorsonDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_dco_NumberofSubsidiariesThatAreNotGuarantorsonDebt_46324147-6ede-4a01-a319-bb1438bc73c4" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_9e83049a-9d22-48da-a5c8-c48431a76860" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_DerivativeNotionalAmount_9e83049a-9d22-48da-a5c8-c48431a76860" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAverageFixedInterestRate_97a49091-7c5e-4087-82fc-b2075b765572" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeAverageFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_DerivativeAverageFixedInterestRate_97a49091-7c5e-4087-82fc-b2075b765572" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_56346a76-20f7-4d92-8c00-a318bba7fa66" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_56346a76-20f7-4d92-8c00-a318bba7fa66" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_ab3f9a70-5c09-441a-b4ac-2b78ab3a5d6b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_ab3f9a70-5c09-441a-b4ac-2b78ab3a5d6b" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_1fa7baed-cb90-4ab4-9d67-35cb923dc839" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_1fa7baed-cb90-4ab4-9d67-35cb923dc839" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_00f16680-3130-445c-bf01-b06f840fbec1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_00f16680-3130-445c-bf01-b06f840fbec1" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1e8d82e7-7812-4158-86a6-adb553802cb1" xlink:to="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_85545d62-ecf1-440a-a68f-0c0a5bcc732f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_us-gaap_CreditFacilityAxis_85545d62-ecf1-440a-a68f-0c0a5bcc732f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_85545d62-ecf1-440a-a68f-0c0a5bcc732f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_85545d62-ecf1-440a-a68f-0c0a5bcc732f" xlink:to="loc_us-gaap_CreditFacilityDomain_85545d62-ecf1-440a-a68f-0c0a5bcc732f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_766d962f-4045-4b48-9f3a-8ef8e757db5f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_85545d62-ecf1-440a-a68f-0c0a5bcc732f" xlink:to="loc_us-gaap_CreditFacilityDomain_766d962f-4045-4b48-9f3a-8ef8e757db5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_f5d23629-f58d-4e0c-82a6-37b2117b4d18" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_766d962f-4045-4b48-9f3a-8ef8e757db5f" xlink:to="loc_us-gaap_SecuredDebtMember_f5d23629-f58d-4e0c-82a6-37b2117b4d18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_955bd8da-182c-474e-a6cb-ada8441b6b90" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_766d962f-4045-4b48-9f3a-8ef8e757db5f" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_955bd8da-182c-474e-a6cb-ada8441b6b90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_118eb8a9-9c02-4a83-b917-5407a5507506" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_us-gaap_DebtInstrumentAxis_118eb8a9-9c02-4a83-b917-5407a5507506" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_118eb8a9-9c02-4a83-b917-5407a5507506_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_118eb8a9-9c02-4a83-b917-5407a5507506" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_118eb8a9-9c02-4a83-b917-5407a5507506_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_118eb8a9-9c02-4a83-b917-5407a5507506" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2022TermLoanMaturingJuly142027Member_4b9a6d91-4e5e-4883-8e8d-f800f8baba2a" xlink:href="dco-20230701.xsd#dco_A2022TermLoanMaturingJuly142027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_A2022TermLoanMaturingJuly142027Member_4b9a6d91-4e5e-4883-8e8d-f800f8baba2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2022RevolvingCreditFacilityDueJuly142027Member_bb744e16-68b8-4b25-871f-ebed7d700b1c" xlink:href="dco-20230701.xsd#dco_A2022RevolvingCreditFacilityDueJuly142027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_A2022RevolvingCreditFacilityDueJuly142027Member_bb744e16-68b8-4b25-871f-ebed7d700b1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2019RevolvingCreditFacilityDueDecember202024Member_0e0eb335-9892-42c1-8849-e6abcb957d63" xlink:href="dco-20230701.xsd#dco_A2019RevolvingCreditFacilityDueDecember202024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_A2019RevolvingCreditFacilityDueDecember202024Member_0e0eb335-9892-42c1-8849-e6abcb957d63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_New2018RevolvingCreditFacilityMaturingNovember212023Member_9a517b4d-2fc1-459a-bbe0-8f4dcbb23b52" xlink:href="dco-20230701.xsd#dco_New2018RevolvingCreditFacilityMaturingNovember212023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_New2018RevolvingCreditFacilityMaturingNovember212023Member_9a517b4d-2fc1-459a-bbe0-8f4dcbb23b52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2019TermLoanMaturingDecember202024Member_8127dbb8-1bea-4fa9-be46-6ca372f01a71" xlink:href="dco-20230701.xsd#dco_A2019TermLoanMaturingDecember202024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_A2019TermLoanMaturingDecember202024Member_8127dbb8-1bea-4fa9-be46-6ca372f01a71" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_New2018TermLoanMaturingNovember212025Member_5d68e83e-3201-4482-a916-d1048a7a2341" xlink:href="dco-20230701.xsd#dco_New2018TermLoanMaturingNovember212025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_New2018TermLoanMaturingNovember212025Member_5d68e83e-3201-4482-a916-d1048a7a2341" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_CreditFacilitiesMember_cf580c2e-a2f2-4562-86ce-2fb06ee57a45" xlink:href="dco-20230701.xsd#dco_CreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_CreditFacilitiesMember_cf580c2e-a2f2-4562-86ce-2fb06ee57a45" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NewCreditFacilitiesMember_c1650ee2-edab-4d79-88f3-51c98604b504" xlink:href="dco-20230701.xsd#dco_NewCreditFacilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_NewCreditFacilitiesMember_c1650ee2-edab-4d79-88f3-51c98604b504" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_OtherInstrumentsMember_56fe235a-5c73-4375-b798-5ebca0d1e945" xlink:href="dco-20230701.xsd#dco_OtherInstrumentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d784db54-42d7-4e37-87dc-3601ef2bf52e" xlink:to="loc_dco_OtherInstrumentsMember_56fe235a-5c73-4375-b798-5ebca0d1e945" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_ef467b95-68ab-48dd-9f6a-7097abf88dd1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_us-gaap_VariableRateAxis_ef467b95-68ab-48dd-9f6a-7097abf88dd1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_ef467b95-68ab-48dd-9f6a-7097abf88dd1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_ef467b95-68ab-48dd-9f6a-7097abf88dd1" xlink:to="loc_us-gaap_VariableRateDomain_ef467b95-68ab-48dd-9f6a-7097abf88dd1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_e7b72f4c-6020-4f0b-9cee-aad54833d21f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_ef467b95-68ab-48dd-9f6a-7097abf88dd1" xlink:to="loc_us-gaap_VariableRateDomain_e7b72f4c-6020-4f0b-9cee-aad54833d21f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_5286a3b7-2539-4465-adf5-7ea472c61c38" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_e7b72f4c-6020-4f0b-9cee-aad54833d21f" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_5286a3b7-2539-4465-adf5-7ea472c61c38" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LondonInterbankOfferedRateLIBOR1Member_24816a87-a722-4764-8241-cbb417c2b39e" xlink:href="dco-20230701.xsd#dco_LondonInterbankOfferedRateLIBOR1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_e7b72f4c-6020-4f0b-9cee-aad54833d21f" xlink:to="loc_dco_LondonInterbankOfferedRateLIBOR1Member_24816a87-a722-4764-8241-cbb417c2b39e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_8955cb95-5622-4db7-9e11-1a63ac9a6884" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_e7b72f4c-6020-4f0b-9cee-aad54833d21f" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_8955cb95-5622-4db7-9e11-1a63ac9a6884" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EurodollarMember_64dc95d8-0463-419c-8afd-efafae781d09" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EurodollarMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_e7b72f4c-6020-4f0b-9cee-aad54833d21f" xlink:to="loc_us-gaap_EurodollarMember_64dc95d8-0463-419c-8afd-efafae781d09" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_8817487a-ed04-4170-b9cb-957fbb85a831" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_e7b72f4c-6020-4f0b-9cee-aad54833d21f" xlink:to="loc_us-gaap_BaseRateMember_8817487a-ed04-4170-b9cb-957fbb85a831" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_c5f994d8-aa78-40e4-a9f3-0bf69a9ea719" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_srt_RangeAxis_c5f994d8-aa78-40e4-a9f3-0bf69a9ea719" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c5f994d8-aa78-40e4-a9f3-0bf69a9ea719_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_c5f994d8-aa78-40e4-a9f3-0bf69a9ea719" xlink:to="loc_srt_RangeMember_c5f994d8-aa78-40e4-a9f3-0bf69a9ea719_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fa37db1d-81fb-433b-b432-c82b879275aa" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_c5f994d8-aa78-40e4-a9f3-0bf69a9ea719" xlink:to="loc_srt_RangeMember_fa37db1d-81fb-433b-b432-c82b879275aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_f83e007e-ef60-4d0a-b511-36de7e77412e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fa37db1d-81fb-433b-b432-c82b879275aa" xlink:to="loc_srt_MinimumMember_f83e007e-ef60-4d0a-b511-36de7e77412e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_f9b718c0-bbfe-4a63-ba1f-898efb957004" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fa37db1d-81fb-433b-b432-c82b879275aa" xlink:to="loc_srt_MaximumMember_f9b718c0-bbfe-4a63-ba1f-898efb957004" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_4095bd26-bd29-4162-8652-bb6c2e4e5994" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_4095bd26-bd29-4162-8652-bb6c2e4e5994" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_4095bd26-bd29-4162-8652-bb6c2e4e5994_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_4095bd26-bd29-4162-8652-bb6c2e4e5994" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_4095bd26-bd29-4162-8652-bb6c2e4e5994_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_ff9b8ec4-51e7-4027-8162-882c3fa618a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_4095bd26-bd29-4162-8652-bb6c2e4e5994" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_ff9b8ec4-51e7-4027-8162-882c3fa618a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_4e0d720b-59bc-4541-aeb2-264763e3cd43" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_ff9b8ec4-51e7-4027-8162-882c3fa618a9" xlink:to="loc_us-gaap_InterestRateSwapMember_4e0d720b-59bc-4541-aeb2-264763e3cd43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentConvenantAxis_db45ddb4-d8f5-4e9c-b1ff-05c43563ca90" xlink:href="dco-20230701.xsd#dco_DebtInstrumentConvenantAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_dco_DebtInstrumentConvenantAxis_db45ddb4-d8f5-4e9c-b1ff-05c43563ca90" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentConvenantDomain_db45ddb4-d8f5-4e9c-b1ff-05c43563ca90_default" xlink:href="dco-20230701.xsd#dco_DebtInstrumentConvenantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dco_DebtInstrumentConvenantAxis_db45ddb4-d8f5-4e9c-b1ff-05c43563ca90" xlink:to="loc_dco_DebtInstrumentConvenantDomain_db45ddb4-d8f5-4e9c-b1ff-05c43563ca90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentConvenantDomain_0d76b809-892c-49b3-b386-a48c1904cbe6" xlink:href="dco-20230701.xsd#dco_DebtInstrumentConvenantDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dco_DebtInstrumentConvenantAxis_db45ddb4-d8f5-4e9c-b1ff-05c43563ca90" xlink:to="loc_dco_DebtInstrumentConvenantDomain_0d76b809-892c-49b3-b386-a48c1904cbe6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenant50OfExcessCashFlowAmountMember_8baadb2e-0cc7-4a4b-b7b7-e59168d0398e" xlink:href="dco-20230701.xsd#dco_DebtInstrumentCovenant50OfExcessCashFlowAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentConvenantDomain_0d76b809-892c-49b3-b386-a48c1904cbe6" xlink:to="loc_dco_DebtInstrumentCovenant50OfExcessCashFlowAmountMember_8baadb2e-0cc7-4a4b-b7b7-e59168d0398e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenant25OfExcessCashFlowAmountMember_0080e811-3a75-4739-8a8a-9bfe635f4724" xlink:href="dco-20230701.xsd#dco_DebtInstrumentCovenant25OfExcessCashFlowAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentConvenantDomain_0d76b809-892c-49b3-b386-a48c1904cbe6" xlink:to="loc_dco_DebtInstrumentCovenant25OfExcessCashFlowAmountMember_0080e811-3a75-4739-8a8a-9bfe635f4724" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentCovenant0OfExcessCashFlowAmountMember_193ade6d-f75a-4887-872a-9c8447c9a5a3" xlink:href="dco-20230701.xsd#dco_DebtInstrumentCovenant0OfExcessCashFlowAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentConvenantDomain_0d76b809-892c-49b3-b386-a48c1904cbe6" xlink:to="loc_dco_DebtInstrumentCovenant0OfExcessCashFlowAmountMember_193ade6d-f75a-4887-872a-9c8447c9a5a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_92b89781-8693-4a9f-ba55-5015291e87eb" xlink:href="dco-20230701.xsd#dco_DebtInstrumentQuarterlyPrepaymentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_92b89781-8693-4a9f-ba55-5015291e87eb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_92b89781-8693-4a9f-ba55-5015291e87eb_default" xlink:href="dco-20230701.xsd#dco_DebtInstrumentQuarterlyPrepaymentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_92b89781-8693-4a9f-ba55-5015291e87eb" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_92b89781-8693-4a9f-ba55-5015291e87eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_4ce7d534-0335-4bba-8d9e-222b72060a00" xlink:href="dco-20230701.xsd#dco_DebtInstrumentQuarterlyPrepaymentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentAxis_92b89781-8693-4a9f-ba55-5015291e87eb" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_4ce7d534-0335-4bba-8d9e-222b72060a00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentYearOneAndYearTwoMember_0be2c1b3-11f4-4dbe-8cab-276fa50d8c41" xlink:href="dco-20230701.xsd#dco_DebtInstrumentQuarterlyPrepaymentYearOneAndYearTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_4ce7d534-0335-4bba-8d9e-222b72060a00" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentYearOneAndYearTwoMember_0be2c1b3-11f4-4dbe-8cab-276fa50d8c41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentYearThreeAndYearFourMember_1c36b8a0-2089-4919-85c7-92cebaeec829" xlink:href="dco-20230701.xsd#dco_DebtInstrumentQuarterlyPrepaymentYearThreeAndYearFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_4ce7d534-0335-4bba-8d9e-222b72060a00" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentYearThreeAndYearFourMember_1c36b8a0-2089-4919-85c7-92cebaeec829" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_DebtInstrumentQuarterlyPrepaymentYearFiveMember_ebddbaf6-596c-4054-90df-179bac438578" xlink:href="dco-20230701.xsd#dco_DebtInstrumentQuarterlyPrepaymentYearFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dco_DebtInstrumentQuarterlyPrepaymentDomain_4ce7d534-0335-4bba-8d9e-222b72060a00" xlink:to="loc_dco_DebtInstrumentQuarterlyPrepaymentYearFiveMember_ebddbaf6-596c-4054-90df-179bac438578" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_d51dadaa-d944-49e2-a46c-78b622f61ebb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_e9c8f132-040e-4f11-9cb4-d8f78e1d2c8f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_d51dadaa-d944-49e2-a46c-78b622f61ebb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d51dadaa-d944-49e2-a46c-78b622f61ebb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d51dadaa-d944-49e2-a46c-78b622f61ebb" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d51dadaa-d944-49e2-a46c-78b622f61ebb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_bcc1505a-9dc5-4b1b-9415-bbc0cf77bd5a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d51dadaa-d944-49e2-a46c-78b622f61ebb" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_bcc1505a-9dc5-4b1b-9415-bbc0cf77bd5a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BLRAerospaceLLCMember_994262f7-f301-42e2-8701-8184daabeeac" xlink:href="dco-20230701.xsd#dco_BLRAerospaceLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_bcc1505a-9dc5-4b1b-9415-bbc0cf77bd5a" xlink:to="loc_dco_BLRAerospaceLLCMember_994262f7-f301-42e2-8701-8184daabeeac" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/ShareholdersEquityDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#ShareholdersEquityDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/ShareholdersEquityDetails" xlink:type="extended" id="iac39ac85cd834f59900d4bcc4ebe65d7_ShareholdersEquityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_24c3a551-2db9-4390-8f00-35ba2f5f32a1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_24c3a551-2db9-4390-8f00-35ba2f5f32a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_6722f3c6-8c51-448f-ba6e-aadda81aa07e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_6722f3c6-8c51-448f-ba6e-aadda81aa07e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_21854adc-e6d1-4e94-a436-c059eeca5550" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_21854adc-e6d1-4e94-a436-c059eeca5550" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_0767bbd1-3782-4e81-8ae1-6153daf1f48d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_0767bbd1-3782-4e81-8ae1-6153daf1f48d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_NetProceedsFromSaleOfStock_85b86b5d-7df8-4ed3-acab-2b57b33ef053" xlink:href="dco-20230701.xsd#dco_NetProceedsFromSaleOfStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_dco_NetProceedsFromSaleOfStock_85b86b5d-7df8-4ed3-acab-2b57b33ef053" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SaleOfStockIncreaseInCommonStockAtParValue_ef462b0f-5f57-4aca-b45c-37756acc42d7" xlink:href="dco-20230701.xsd#dco_SaleOfStockIncreaseInCommonStockAtParValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_dco_SaleOfStockIncreaseInCommonStockAtParValue_ef462b0f-5f57-4aca-b45c-37756acc42d7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_SaleOfStockIncreaseInAdditionalPaidInCapital_aa33e3d6-6d98-4e8d-9560-9d2201504218" xlink:href="dco-20230701.xsd#dco_SaleOfStockIncreaseInAdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_dco_SaleOfStockIncreaseInAdditionalPaidInCapital_aa33e3d6-6d98-4e8d-9560-9d2201504218" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_41beed2b-8564-4522-97bf-c0b627957de0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_41beed2b-8564-4522-97bf-c0b627957de0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_5d9737fc-c377-4dd7-9e7d-5e0e226adc1e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_889a7f5f-ff3f-4aff-9428-4be2d3efe8d8" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_5d9737fc-c377-4dd7-9e7d-5e0e226adc1e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_1a1cc623-5271-4acb-b99e-574848bd24e7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_5d9737fc-c377-4dd7-9e7d-5e0e226adc1e" xlink:to="loc_us-gaap_CreditFacilityAxis_1a1cc623-5271-4acb-b99e-574848bd24e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_1a1cc623-5271-4acb-b99e-574848bd24e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_1a1cc623-5271-4acb-b99e-574848bd24e7" xlink:to="loc_us-gaap_CreditFacilityDomain_1a1cc623-5271-4acb-b99e-574848bd24e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_950588e3-0010-4e68-bb0c-65617040ee83" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_1a1cc623-5271-4acb-b99e-574848bd24e7" xlink:to="loc_us-gaap_CreditFacilityDomain_950588e3-0010-4e68-bb0c-65617040ee83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_c2bf2733-def7-41bc-b029-b4357f2075d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_950588e3-0010-4e68-bb0c-65617040ee83" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_c2bf2733-def7-41bc-b029-b4357f2075d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_A2022RevolvingCreditFacilityMember_120ce6a9-8d60-4250-ba78-92092dbf1a7b" xlink:href="dco-20230701.xsd#dco_A2022RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_950588e3-0010-4e68-bb0c-65617040ee83" xlink:to="loc_dco_A2022RevolvingCreditFacilityMember_120ce6a9-8d60-4250-ba78-92092dbf1a7b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="idae3e534b5a34bb488cb40147c9f992a_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationReserve_62d86354-aa4d-4067-ac2d-d9d01b7d367f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LitigationReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_LitigationReserve_62d86354-aa4d-4067-ac2d-d9d01b7d367f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease_77ab9c35-4c1c-49a7-966f-8e0805cbf59e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease_77ab9c35-4c1c-49a7-966f-8e0805cbf59e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForLegalSettlements_4cf0b213-3fb4-4cdb-81c4-4144ee3bac31" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsForLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_PaymentsForLegalSettlements_4cf0b213-3fb4-4cdb-81c4-4144ee3bac31" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyAccrualAtCarryingValue_55c789e9-b99c-42d3-bdac-7b95d6fcf555" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyAccrualAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_LossContingencyAccrualAtCarryingValue_55c789e9-b99c-42d3-bdac-7b95d6fcf555" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_14d02a0a-8102-48e7-9a07-16bb0c1faa7e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_14d02a0a-8102-48e7-9a07-16bb0c1faa7e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LossContingencyNumberOfBuildingsAffected_f4766e60-4f2f-475f-bfb6-b4882975ad2b" xlink:href="dco-20230701.xsd#dco_LossContingencyNumberOfBuildingsAffected"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_dco_LossContingencyNumberOfBuildingsAffected_f4766e60-4f2f-475f-bfb6-b4882975ad2b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AreaOfRealEstateProperty_84c9f16c-a0cd-4dbc-8b23-e36885bca6d7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AreaOfRealEstateProperty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_AreaOfRealEstateProperty_84c9f16c-a0cd-4dbc-8b23-e36885bca6d7" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f3799470-c21d-4c47-bb13-e0c75c606b5b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f3799470-c21d-4c47-bb13-e0c75c606b5b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_1e506add-b29d-4b7c-a527-615b0cdb8978" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_1e506add-b29d-4b7c-a527-615b0cdb8978" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleCarryingValueOfAsset_dc0ac093-51a7-4dd0-86f0-30492995a1bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleCarryingValueOfAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleCarryingValueOfAsset_dc0ac093-51a7-4dd0-86f0-30492995a1bf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyReceivableProceeds_5ffec05e-c35d-4771-ad49-a625d04a9cc7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyReceivableProceeds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_LossContingencyReceivableProceeds_5ffec05e-c35d-4771-ad49-a625d04a9cc7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LossContingencyReceivableProceedsReceivedToDate_147e6ad2-11b9-4caf-b783-bad799c30742" xlink:href="dco-20230701.xsd#dco_LossContingencyReceivableProceedsReceivedToDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_dco_LossContingencyReceivableProceedsReceivedToDate_147e6ad2-11b9-4caf-b783-bad799c30742" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LossContingencyPropertyAndEquipmentWriteOff_1a5b86d8-834e-4492-b15b-5423335b210b" xlink:href="dco-20230701.xsd#dco_LossContingencyPropertyAndEquipmentWriteOff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_dco_LossContingencyPropertyAndEquipmentWriteOff_1a5b86d8-834e-4492-b15b-5423335b210b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LossContingencyDeductibleAmount_a8f06859-d326-4837-a312-98b5d2a260b4" xlink:href="dco-20230701.xsd#dco_LossContingencyDeductibleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_dco_LossContingencyDeductibleAmount_a8f06859-d326-4837-a312-98b5d2a260b4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_6d971cd8-3368-415b-b0c4-aefb88cc260c" xlink:to="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_e5bdb635-d7f9-4c45-810a-f90224700e00" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_e5bdb635-d7f9-4c45-810a-f90224700e00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_e5bdb635-d7f9-4c45-810a-f90224700e00_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_e5bdb635-d7f9-4c45-810a-f90224700e00" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_e5bdb635-d7f9-4c45-810a-f90224700e00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_b7f25fbf-c1e9-46de-9ba7-d7fbc34c2feb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_e5bdb635-d7f9-4c45-810a-f90224700e00" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_b7f25fbf-c1e9-46de-9ba7-d7fbc34c2feb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesMember_ce5eeb3d-e9af-4e3b-ac53-74f7fe1702c7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_b7f25fbf-c1e9-46de-9ba7-d7fbc34c2feb" xlink:to="loc_us-gaap_AccruedLiabilitiesMember_ce5eeb3d-e9af-4e3b-ac53-74f7fe1702c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_cb096b4f-568d-419a-a782-1bbfa6334ace" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:to="loc_srt_StatementGeographicalAxis_cb096b4f-568d-419a-a782-1bbfa6334ace" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_cb096b4f-568d-419a-a782-1bbfa6334ace_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_cb096b4f-568d-419a-a782-1bbfa6334ace" xlink:to="loc_srt_SegmentGeographicalDomain_cb096b4f-568d-419a-a782-1bbfa6334ace_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_563b0a3b-2789-49a0-b008-7daf413f8ac7" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_cb096b4f-568d-419a-a782-1bbfa6334ace" xlink:to="loc_srt_SegmentGeographicalDomain_563b0a3b-2789-49a0-b008-7daf413f8ac7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LocationOneMember_45456d14-dee0-4fcf-9b9a-3aa64c3e144c" xlink:href="dco-20230701.xsd#dco_LocationOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_563b0a3b-2789-49a0-b008-7daf413f8ac7" xlink:to="loc_dco_LocationOneMember_45456d14-dee0-4fcf-9b9a-3aa64c3e144c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_LocationTwoMember_e8b2f9c5-87dc-4371-a0bb-5117e19038b5" xlink:href="dco-20230701.xsd#dco_LocationTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_563b0a3b-2789-49a0-b008-7daf413f8ac7" xlink:to="loc_dco_LocationTwoMember_e8b2f9c5-87dc-4371-a0bb-5117e19038b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GuaymasMexicoMember_ef044350-821c-4ef1-87c0-52deed36529a" xlink:href="dco-20230701.xsd#dco_GuaymasMexicoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_563b0a3b-2789-49a0-b008-7daf413f8ac7" xlink:to="loc_dco_GuaymasMexicoMember_ef044350-821c-4ef1-87c0-52deed36529a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_32063fb2-3f5c-48c2-8cc8-19975bec5a59" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_32063fb2-3f5c-48c2-8cc8-19975bec5a59" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_32063fb2-3f5c-48c2-8cc8-19975bec5a59_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_32063fb2-3f5c-48c2-8cc8-19975bec5a59" xlink:to="loc_us-gaap_SegmentDomain_32063fb2-3f5c-48c2-8cc8-19975bec5a59_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_63f0ab7c-9309-4d8a-9c21-25ccb02214bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_32063fb2-3f5c-48c2-8cc8-19975bec5a59" xlink:to="loc_us-gaap_SegmentDomain_63f0ab7c-9309-4d8a-9c21-25ccb02214bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsMember_d403a94f-bd49-473a-8756-40d6b160f31d" xlink:href="dco-20230701.xsd#dco_StructuralSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_63f0ab7c-9309-4d8a-9c21-25ccb02214bf" xlink:to="loc_dco_StructuralSystemsMember_d403a94f-bd49-473a-8756-40d6b160f31d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_0f8f9b21-a228-44cd-b699-295271c1f70f" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:to="loc_srt_RangeAxis_0f8f9b21-a228-44cd-b699-295271c1f70f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0f8f9b21-a228-44cd-b699-295271c1f70f_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_0f8f9b21-a228-44cd-b699-295271c1f70f" xlink:to="loc_srt_RangeMember_0f8f9b21-a228-44cd-b699-295271c1f70f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_55258069-b19e-4e6d-905d-1da651b16d69" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_0f8f9b21-a228-44cd-b699-295271c1f70f" xlink:to="loc_srt_RangeMember_55258069-b19e-4e6d-905d-1da651b16d69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3e442d81-5fae-4c92-bd4b-a7f0e67d8789" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_55258069-b19e-4e6d-905d-1da651b16d69" xlink:to="loc_srt_MinimumMember_3e442d81-5fae-4c92-bd4b-a7f0e67d8789" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_4134fca5-d6a3-4ca3-87b8-3e050aa2af7c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_55258069-b19e-4e6d-905d-1da651b16d69" xlink:to="loc_srt_MaximumMember_4134fca5-d6a3-4ca3-87b8-3e050aa2af7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_be19879c-89bd-4e1e-8827-694d46397b60" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_be19879c-89bd-4e1e-8827-694d46397b60" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_be19879c-89bd-4e1e-8827-694d46397b60_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_be19879c-89bd-4e1e-8827-694d46397b60" xlink:to="loc_us-gaap_LossContingencyNatureDomain_be19879c-89bd-4e1e-8827-694d46397b60_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_7c29a0ea-0393-4510-8e2d-81095bad5074" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_be19879c-89bd-4e1e-8827-694d46397b60" xlink:to="loc_us-gaap_LossContingencyNatureDomain_7c29a0ea-0393-4510-8e2d-81095bad5074" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DamageFromFireExplosionOrOtherHazardMember_58f9eccd-d893-42ff-901f-a247026f96dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DamageFromFireExplosionOrOtherHazardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_7c29a0ea-0393-4510-8e2d-81095bad5074" xlink:to="loc_us-gaap_DamageFromFireExplosionOrOtherHazardMember_58f9eccd-d893-42ff-901f-a247026f96dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BusinessInterruptionMember_204ea897-d871-4a62-8682-414f67578ee7" xlink:href="dco-20230701.xsd#dco_BusinessInterruptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_7c29a0ea-0393-4510-8e2d-81095bad5074" xlink:to="loc_dco_BusinessInterruptionMember_204ea897-d871-4a62-8682-414f67578ee7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PropertyEquipmentInventoriesAndToolingMember_a434efef-c431-4e1d-969d-5108eeaf0e43" xlink:href="dco-20230701.xsd#dco_PropertyEquipmentInventoriesAndToolingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_7c29a0ea-0393-4510-8e2d-81095bad5074" xlink:to="loc_dco_PropertyEquipmentInventoriesAndToolingMember_a434efef-c431-4e1d-969d-5108eeaf0e43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_2066a221-2390-4ac4-a10c-8a8e3b916ee4" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:to="loc_srt_RestatementAxis_2066a221-2390-4ac4-a10c-8a8e3b916ee4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_2066a221-2390-4ac4-a10c-8a8e3b916ee4_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_2066a221-2390-4ac4-a10c-8a8e3b916ee4" xlink:to="loc_srt_RestatementDomain_2066a221-2390-4ac4-a10c-8a8e3b916ee4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_0cb89a1e-27b9-4ec2-9862-21a9b7e5c53a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_2066a221-2390-4ac4-a10c-8a8e3b916ee4" xlink:to="loc_srt_RestatementDomain_0cb89a1e-27b9-4ec2-9862-21a9b7e5c53a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RevisionOfPriorPeriodReclassificationAdjustmentMember_3c2e5b5d-d7b6-472a-a573-a0d861f88dde" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RevisionOfPriorPeriodReclassificationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_0cb89a1e-27b9-4ec2-9862-21a9b7e5c53a" xlink:to="loc_srt_RevisionOfPriorPeriodReclassificationAdjustmentMember_3c2e5b5d-d7b6-472a-a573-a0d861f88dde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_c2f2914d-556c-4de9-926b-d623756b7537" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ff05b081-5e5c-4cd5-873a-eb3d0985eaf6" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_c2f2914d-556c-4de9-926b-d623756b7537" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_c2f2914d-556c-4de9-926b-d623756b7537_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_c2f2914d-556c-4de9-926b-d623756b7537" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_c2f2914d-556c-4de9-926b-d623756b7537_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_7b759710-61ae-4244-b18c-bce0f6f3b1d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_c2f2914d-556c-4de9-926b-d623756b7537" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_7b759710-61ae-4244-b18c-bce0f6f3b1d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentMember_a44698a9-70f1-4d4d-a9ca-ab6a8fcd9151" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_7b759710-61ae-4244-b18c-bce0f6f3b1d8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentMember_a44698a9-70f1-4d4d-a9ca-ab6a8fcd9151" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoriesMember_ac1d6a83-069b-4085-8c83-f95deaa755ad" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InventoriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_7b759710-61ae-4244-b18c-bce0f6f3b1d8" xlink:to="loc_us-gaap_InventoriesMember_ac1d6a83-069b-4085-8c83-f95deaa755ad" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails" xlink:type="extended" id="i40941da4d6d54c098d1959aae8b48d74_BusinessSegmentInformationFinancialInformationbyReportableSegmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_e2ca0664-53d7-4853-85e0-dee0e16b407c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f2e88da8-6776-4b0f-9218-906d7e4de692" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e2ca0664-53d7-4853-85e0-dee0e16b407c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_f2e88da8-6776-4b0f-9218-906d7e4de692" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_44b409cc-3277-4892-bba5-0a070774a777" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e2ca0664-53d7-4853-85e0-dee0e16b407c" xlink:to="loc_us-gaap_OperatingIncomeLoss_44b409cc-3277-4892-bba5-0a070774a777" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_b57e5fa5-b69e-4dd9-acb7-eb7ea14b7974" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e2ca0664-53d7-4853-85e0-dee0e16b407c" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_b57e5fa5-b69e-4dd9-acb7-eb7ea14b7974" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_7c7aeada-98cf-452d-9691-57a2d77a251b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e2ca0664-53d7-4853-85e0-dee0e16b407c" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_7c7aeada-98cf-452d-9691-57a2d77a251b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_CapitalExpenditures_e624ee18-6566-4bba-9e82-846b20752617" xlink:href="dco-20230701.xsd#dco_CapitalExpenditures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e2ca0664-53d7-4853-85e0-dee0e16b407c" xlink:to="loc_dco_CapitalExpenditures_e624ee18-6566-4bba-9e82-846b20752617" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_fcdd2cb5-fa79-4b49-a0f3-0c3a8a9e5939" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e2ca0664-53d7-4853-85e0-dee0e16b407c" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_fcdd2cb5-fa79-4b49-a0f3-0c3a8a9e5939" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_ea198596-d379-48e4-b7ec-1cef6d6db971" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_fcdd2cb5-fa79-4b49-a0f3-0c3a8a9e5939" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_ea198596-d379-48e4-b7ec-1cef6d6db971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_ea198596-d379-48e4-b7ec-1cef6d6db971_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ea198596-d379-48e4-b7ec-1cef6d6db971" xlink:to="loc_us-gaap_SegmentDomain_ea198596-d379-48e4-b7ec-1cef6d6db971_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_aef2cd8f-ce9f-4f9e-8673-b9f360b15cc1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ea198596-d379-48e4-b7ec-1cef6d6db971" xlink:to="loc_us-gaap_SegmentDomain_aef2cd8f-ce9f-4f9e-8673-b9f360b15cc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsMember_aa6f5ec4-7302-42a4-b803-2f37fa6406ea" xlink:href="dco-20230701.xsd#dco_ElectronicSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_aef2cd8f-ce9f-4f9e-8673-b9f360b15cc1" xlink:to="loc_dco_ElectronicSystemsMember_aa6f5ec4-7302-42a4-b803-2f37fa6406ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsMember_17847c3a-4cf9-4e13-931f-8bc28775355d" xlink:href="dco-20230701.xsd#dco_StructuralSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_aef2cd8f-ce9f-4f9e-8673-b9f360b15cc1" xlink:to="loc_dco_StructuralSystemsMember_17847c3a-4cf9-4e13-931f-8bc28775355d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_6d89f7fe-5275-4380-b95e-d3037f963c35" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_fcdd2cb5-fa79-4b49-a0f3-0c3a8a9e5939" xlink:to="loc_srt_ConsolidationItemsAxis_6d89f7fe-5275-4380-b95e-d3037f963c35" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_6d89f7fe-5275-4380-b95e-d3037f963c35_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_6d89f7fe-5275-4380-b95e-d3037f963c35" xlink:to="loc_srt_ConsolidationItemsDomain_6d89f7fe-5275-4380-b95e-d3037f963c35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_dc729f35-cf00-4113-811d-f0b34a3d6359" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_6d89f7fe-5275-4380-b95e-d3037f963c35" xlink:to="loc_srt_ConsolidationItemsDomain_dc729f35-cf00-4113-811d-f0b34a3d6359" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_1004ed83-6ed8-4a8d-a78b-8e8a6161780a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_dc729f35-cf00-4113-811d-f0b34a3d6359" xlink:to="loc_us-gaap_OperatingSegmentsMember_1004ed83-6ed8-4a8d-a78b-8e8a6161780a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_44f9d9d2-4712-4c05-a6c7-4a3635832b78" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_dc729f35-cf00-4113-811d-f0b34a3d6359" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_44f9d9d2-4712-4c05-a6c7-4a3635832b78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_f53ce5e1-5c4c-4798-812e-813d6a2ab495" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_dc729f35-cf00-4113-811d-f0b34a3d6359" xlink:to="loc_us-gaap_CorporateNonSegmentMember_f53ce5e1-5c4c-4798-812e-813d6a2ab495" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ducommun.com/role/BusinessSegmentInformationSegmentAssetsDetails" xlink:type="simple" xlink:href="dco-20230701.xsd#BusinessSegmentInformationSegmentAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.ducommun.com/role/BusinessSegmentInformationSegmentAssetsDetails" xlink:type="extended" id="id275af2f29f3490393ebea063c142584_BusinessSegmentInformationSegmentAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_c080ac1c-3daf-4d58-a9df-9ec8669e6437" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_966321eb-6cc5-46a0-9a8c-a59f6dd97df7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c080ac1c-3daf-4d58-a9df-9ec8669e6437" xlink:to="loc_us-gaap_Assets_966321eb-6cc5-46a0-9a8c-a59f6dd97df7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_GoodwillAndOtherIntangibleAssets_2cdc8392-e057-4e9a-bd42-a390b51f1417" xlink:href="dco-20230701.xsd#dco_GoodwillAndOtherIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c080ac1c-3daf-4d58-a9df-9ec8669e6437" xlink:to="loc_dco_GoodwillAndOtherIntangibleAssets_2cdc8392-e057-4e9a-bd42-a390b51f1417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_PercentageOfOutstandingEquityInterestsAcquired_1b676033-1c3b-4f87-8f2b-19903c560212" xlink:href="dco-20230701.xsd#dco_PercentageOfOutstandingEquityInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c080ac1c-3daf-4d58-a9df-9ec8669e6437" xlink:to="loc_dco_PercentageOfOutstandingEquityInterestsAcquired_1b676033-1c3b-4f87-8f2b-19903c560212" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_19473bbf-269d-41d6-a04c-ce4fc7777ae4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c080ac1c-3daf-4d58-a9df-9ec8669e6437" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_19473bbf-269d-41d6-a04c-ce4fc7777ae4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_7b00e9d4-5326-4745-8b11-ad9fccd30206" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c080ac1c-3daf-4d58-a9df-9ec8669e6437" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_7b00e9d4-5326-4745-8b11-ad9fccd30206" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_328bdd50-3893-4f27-9ca2-7317a6377eea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_c080ac1c-3daf-4d58-a9df-9ec8669e6437" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_328bdd50-3893-4f27-9ca2-7317a6377eea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_18ad0be7-6f8a-402c-9a0c-675b8bfcbeab" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_328bdd50-3893-4f27-9ca2-7317a6377eea" xlink:to="loc_srt_ConsolidationItemsAxis_18ad0be7-6f8a-402c-9a0c-675b8bfcbeab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_18ad0be7-6f8a-402c-9a0c-675b8bfcbeab_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_18ad0be7-6f8a-402c-9a0c-675b8bfcbeab" xlink:to="loc_srt_ConsolidationItemsDomain_18ad0be7-6f8a-402c-9a0c-675b8bfcbeab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_cddad5c3-ea4f-4927-9163-30d97e05ae98" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_18ad0be7-6f8a-402c-9a0c-675b8bfcbeab" xlink:to="loc_srt_ConsolidationItemsDomain_cddad5c3-ea4f-4927-9163-30d97e05ae98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_b3dfafb1-284a-434c-9c60-8deaa70226dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_cddad5c3-ea4f-4927-9163-30d97e05ae98" xlink:to="loc_us-gaap_OperatingSegmentsMember_b3dfafb1-284a-434c-9c60-8deaa70226dd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_4a25ee87-b99e-4dc2-8d4e-c5c110c41324" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_cddad5c3-ea4f-4927-9163-30d97e05ae98" xlink:to="loc_us-gaap_CorporateNonSegmentMember_4a25ee87-b99e-4dc2-8d4e-c5c110c41324" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_a517c250-997e-4875-bea6-31c2f54b7d00" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_328bdd50-3893-4f27-9ca2-7317a6377eea" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_a517c250-997e-4875-bea6-31c2f54b7d00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_a517c250-997e-4875-bea6-31c2f54b7d00_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_a517c250-997e-4875-bea6-31c2f54b7d00" xlink:to="loc_us-gaap_SegmentDomain_a517c250-997e-4875-bea6-31c2f54b7d00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4be31884-552d-4321-9ebc-8f36c57b6460" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_a517c250-997e-4875-bea6-31c2f54b7d00" xlink:to="loc_us-gaap_SegmentDomain_4be31884-552d-4321-9ebc-8f36c57b6460" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_ElectronicSystemsMember_32500e3a-3afa-4906-88f1-2ac8c6736a51" xlink:href="dco-20230701.xsd#dco_ElectronicSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4be31884-552d-4321-9ebc-8f36c57b6460" xlink:to="loc_dco_ElectronicSystemsMember_32500e3a-3afa-4906-88f1-2ac8c6736a51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_StructuralSystemsMember_df182954-945c-4ed8-9786-6a30e9a9dc21" xlink:href="dco-20230701.xsd#dco_StructuralSystemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4be31884-552d-4321-9ebc-8f36c57b6460" xlink:to="loc_dco_StructuralSystemsMember_df182954-945c-4ed8-9786-6a30e9a9dc21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_28efb4ed-72df-40b5-8404-a4b11b86fd60" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_328bdd50-3893-4f27-9ca2-7317a6377eea" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_28efb4ed-72df-40b5-8404-a4b11b86fd60" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_28efb4ed-72df-40b5-8404-a4b11b86fd60_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_28efb4ed-72df-40b5-8404-a4b11b86fd60" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_28efb4ed-72df-40b5-8404-a4b11b86fd60_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_15b588da-4d53-4256-a2fb-1e5dd036c3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_28efb4ed-72df-40b5-8404-a4b11b86fd60" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_15b588da-4d53-4256-a2fb-1e5dd036c3f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dco_BLRAerospaceLLCMember_5b19c85c-54e6-4723-8ee1-ea3642ce2abf" xlink:href="dco-20230701.xsd#dco_BLRAerospaceLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_15b588da-4d53-4256-a2fb-1e5dd036c3f4" xlink:to="loc_dco_BLRAerospaceLLCMember_5b19c85c-54e6-4723-8ee1-ea3642ce2abf" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
