Definition of undo verb from the Oxford Advanced American Dictionary

      

    undo

     verb
    verb
    NAmE//ʌnˈdu//
     
    Verb Forms present simple I / you / we / they undo
     
    he / she / it undoes
     
    past simple undid
     
    past participle undone
     
    -ing form undoing
     
     
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  1. 1undo something to open something that is fastened, tied or wrapped to undo a button/knot/zip, etc. to undo a jacket/shirt, etc. I undid the package and took out the books. opposite do up
  2. 2undo something to cancel the effect of something He undid most of the good work of the previous manager. It's not too late to try and undo some of the damage. UNDO (= a command on a computer that cancels the previous action)
  3. 3[usually passive] undo somebody/something (formal) to make someone or something fail The team was undone by the speed and strength of their opponents.
See the Oxford Advanced Learner's Dictionary entry: undo