(UNFASTEN) [verb] [T] undoing, [past simple] undid, [past participle] undone - to unfasten (something that is fastened or tied)Can someone help me to undo my seat belt?I'd eaten so much that I had to undo my belt by a couple of holes.
UNDO
Meaning of UNDO in English
Cambridge English vocab. Кембриджский английский словарь. 2012