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English definition of “undo”

undo

verb [T]  /ʌnˈdu/ (present participle undoing, past tense undid  /ʌnˈdɪd/, past participle undone  /ʌnˈdʌn/) us  

undo verb [T] (UNFASTEN)

to unfasten something that is closed or tied: He undid the top button of his shirt and loosened his tie.

undo verb [T] (REMOVE EFFECTS)

to remove the effects of something that happened earlier: It’s difficult to undo the damage caused by a father who abandons his child.
(Definition of undo from the Cambridge Academic Content Dictionary © Cambridge University Press)
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