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English definition of “undo”

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undo

verb [T]
 
 
/ʌnˈduː/ ( present participle undoing, past tense undid, past participle undone)
OPEN B2 to open something that is tied or fastened: I took off my hat and undid my coat. Can you undo this knot for me?Unfastening and opening
GET RID OF EFFECTS B2 to get rid of the effects of something that has been done before: Some of the damage caused by pollution cannot be undone.Removing and getting rid of thingsTaking things away from someone or somewhere
(Definition of undo from the Cambridge Learners Dictionary © Cambridge University Press)
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