undoPronunciation: /ʌnˈduː/Translate undo | into French | into German | into Italian | into Spanish Definition of undo verb (undoes, undoing; past undid; past participle undone) [with object] 1unfasten, untie, or loosen (something):the knot was difficult to undo 2cancel or reverse the effects or results of (a previous action or measure):there wasn’t any way Evelyn could undo the damage cancel (the last command executed by a computer): you can frequently undo the error if you notice it in time 3 formal cause the downfall or ruin of:Iago’s hatred of women undoes him noun Computing a feature of a computer program that allows a user to cancel or reverse the last command executed: [as modifier]:the undo commandOrigin: Old English undōn (see un-2, do1)undo in other Oxford dictionaries Definition of undo in the US English dictionary