undo /ʌnˈduː/verb 4noun 1forms 8 verb4 •To reverse the effects of an action.Fortunately, we can undo most of the damage to the system by the war.What's done can't be undone. •To unfasten.Could you undo my buckle for me? •(informal) To unfasten the clothing of (a person).PROSTITUTE: Undo me. There's a dear. — 1971 •(figurative) To impoverish or ruin, as in reputation; to cause the downfall of.Woe is me, for I am undone! — 1611 noun1 •An operation that reverses a previous action.How many undos does this program support? formsundoed · undid · undone · undoing · undoes · undoeth · undoest · undos