<?xml version="1.0" encoding="utf-8"?>
<!--XBRL document created with Toppan Merrill Bridge  11.2.0.5 -->
<!--Based on XBRL 2.1-->
<!--Created on: 4/7/2026 8:42:34 PM-->
<!--Modified on: 4/7/2026 8:42:34 PM-->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly" />
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpAdjustmentsOnly" />
  <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/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: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://www.esma.europa.eu/xbrl/esef/arcrole/wider-narrower" xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/arcrole/esma-arcrole-2018-11-21.xsd#wider-narrower" />
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended" xlink:title="Individuals">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllIndividualsMember" xlink:label="ecd_AllIndividualsMember" xlink:title="ecd_AllIndividualsMember" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_ScottKirbyMember" xlink:label="ual_ScottKirbyMember" xlink:title="ual_ScottKirbyMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ecd_AllIndividualsMember" xlink:to="ual_ScottKirbyMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ecd_AllIndividualsMember To ual_ScottKirbyMember" order="1" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_OscarMunozMember" xlink:label="ual_OscarMunozMember" xlink:title="ual_OscarMunozMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ecd_AllIndividualsMember" xlink:to="ual_OscarMunozMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ecd_AllIndividualsMember To ual_OscarMunozMember" order="2" priority="0" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="extended" xlink:title="Pay vs Performance Adjustments">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllAdjToCompMember" xlink:label="ecd_AllAdjToCompMember" xlink:title="ecd_AllAdjToCompMember" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_PensionValueInCompensationTableForTheApplicableYearMember" xlink:label="ual_PensionValueInCompensationTableForTheApplicableYearMember" xlink:title="ual_PensionValueInCompensationTableForTheApplicableYearMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ecd_AllAdjToCompMember" xlink:to="ual_PensionValueInCompensationTableForTheApplicableYearMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ecd_AllAdjToCompMember To ual_PensionValueInCompensationTableForTheApplicableYearMember" order="1" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_PensionAdjustmentsMember" xlink:label="ual_PensionAdjustmentsMember" xlink:title="ual_PensionAdjustmentsMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ecd_AllAdjToCompMember" xlink:to="ual_PensionAdjustmentsMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ecd_AllAdjToCompMember To ual_PensionAdjustmentsMember" order="2" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_PensionAdjustmentsServiceCostMember" xlink:label="ual_PensionAdjustmentsServiceCostMember" xlink:title="ual_PensionAdjustmentsServiceCostMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_PensionAdjustmentsMember" xlink:to="ual_PensionAdjustmentsServiceCostMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_PensionAdjustmentsMember To ual_PensionAdjustmentsServiceCostMember" order="1" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_PensionAdjustmentsPriorServiceCostMember" xlink:label="ual_PensionAdjustmentsPriorServiceCostMember" xlink:title="ual_PensionAdjustmentsPriorServiceCostMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_PensionAdjustmentsMember" xlink:to="ual_PensionAdjustmentsPriorServiceCostMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_PensionAdjustmentsMember To ual_PensionAdjustmentsPriorServiceCostMember" order="2" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_NetAdjustmentsForEquityAwardsMember" xlink:label="ual_NetAdjustmentsForEquityAwardsMember" xlink:title="ual_NetAdjustmentsForEquityAwardsMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ecd_AllAdjToCompMember" xlink:to="ual_NetAdjustmentsForEquityAwardsMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ecd_AllAdjToCompMember To ual_NetAdjustmentsForEquityAwardsMember" order="3" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsValueInCompensationTableForTheApplicableYearMember" xlink:label="ual_EquityAwardsValueInCompensationTableForTheApplicableYearMember" xlink:title="ual_EquityAwardsValueInCompensationTableForTheApplicableYearMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_NetAdjustmentsForEquityAwardsMember" xlink:to="ual_EquityAwardsValueInCompensationTableForTheApplicableYearMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_NetAdjustmentsForEquityAwardsMember To ual_EquityAwardsValueInCompensationTableForTheApplicableYearMember" order="1" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsMember" xlink:label="ual_EquityAwardsAdjustmentsMember" xlink:title="ual_EquityAwardsAdjustmentsMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_NetAdjustmentsForEquityAwardsMember" xlink:to="ual_EquityAwardsAdjustmentsMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_NetAdjustmentsForEquityAwardsMember To ual_EquityAwardsAdjustmentsMember" order="2" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsYearEndFairValueOfAwardsGrantedInCurrentYearMember" xlink:label="ual_EquityAwardsAdjustmentsYearEndFairValueOfAwardsGrantedInCurrentYearMember" xlink:title="ual_EquityAwardsAdjustmentsYearEndFairValueOfAwardsGrantedInCurrentYearMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_EquityAwardsAdjustmentsMember" xlink:to="ual_EquityAwardsAdjustmentsYearEndFairValueOfAwardsGrantedInCurrentYearMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_EquityAwardsAdjustmentsMember To ual_EquityAwardsAdjustmentsYearEndFairValueOfAwardsGrantedInCurrentYearMember" order="1" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsChangeInFairValueAsOfYearEndOfOutstandingAndUnvestedAwardsGrantedInPriorYearsMember" xlink:label="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfYearEndOfOutstandingAndUnvestedAwardsGrantedInPriorYearsMember" xlink:title="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfYearEndOfOutstandingAndUnvestedAwardsGrantedInPriorYearsMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_EquityAwardsAdjustmentsMember" xlink:to="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfYearEndOfOutstandingAndUnvestedAwardsGrantedInPriorYearsMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_EquityAwardsAdjustmentsMember To ual_EquityAwardsAdjustmentsChangeInFairValueAsOfYearEndOfOutstandingAndUnvestedAwardsGrantedInPriorYearsMember" order="2" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember" xlink:label="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember" xlink:title="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_EquityAwardsAdjustmentsMember" xlink:to="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_EquityAwardsAdjustmentsMember To ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember" order="3" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfPriorYearAwardsVestedDuringCurrentYearMember" xlink:label="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfPriorYearAwardsVestedDuringCurrentYearMember" xlink:title="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfPriorYearAwardsVestedDuringCurrentYearMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember" xlink:to="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfPriorYearAwardsVestedDuringCurrentYearMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember To ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfPriorYearAwardsVestedDuringCurrentYearMember" order="1" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfCurrentAwardsVestedDuringCurrentYearMember" xlink:label="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfCurrentAwardsVestedDuringCurrentYearMember" xlink:title="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfCurrentAwardsVestedDuringCurrentYearMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember" xlink:to="ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfCurrentAwardsVestedDuringCurrentYearMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfVestedAwardsDuringCurrentYearMember To ual_EquityAwardsAdjustmentsChangeInFairValueAsOfVestingDateOfCurrentAwardsVestedDuringCurrentYearMember" order="2" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsAdjustmentsForEquityAwardsFailedToMeetPerformanceConditionsMember" xlink:label="ual_EquityAwardsAdjustmentsAdjustmentsForEquityAwardsFailedToMeetPerformanceConditionsMember" xlink:title="ual_EquityAwardsAdjustmentsAdjustmentsForEquityAwardsFailedToMeetPerformanceConditionsMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_EquityAwardsAdjustmentsMember" xlink:to="ual_EquityAwardsAdjustmentsAdjustmentsForEquityAwardsFailedToMeetPerformanceConditionsMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_EquityAwardsAdjustmentsMember To ual_EquityAwardsAdjustmentsAdjustmentsForEquityAwardsFailedToMeetPerformanceConditionsMember" order="4" priority="0" />
    <link:loc xlink:type="locator" xlink:href="tmb-20260519.xsd#ual_EquityAwardsAdjustmentsDividendsOrOtherEarningsPaidOnEquityAwardsNotOtherwiseReflectedInFairValueMember" xlink:label="ual_EquityAwardsAdjustmentsDividendsOrOtherEarningsPaidOnEquityAwardsNotOtherwiseReflectedInFairValueMember" xlink:title="ual_EquityAwardsAdjustmentsDividendsOrOtherEarningsPaidOnEquityAwardsNotOtherwiseReflectedInFairValueMember" />
    <link:definitionArc xlink:type="arc" xlink:from="ual_EquityAwardsAdjustmentsMember" xlink:to="ual_EquityAwardsAdjustmentsDividendsOrOtherEarningsPaidOnEquityAwardsNotOtherwiseReflectedInFairValueMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:ual_EquityAwardsAdjustmentsMember To ual_EquityAwardsAdjustmentsDividendsOrOtherEarningsPaidOnEquityAwardsNotOtherwiseReflectedInFairValueMember" order="5" priority="0" />
  </link:definitionLink>
</link:linkbase>
