[verb] - to take (a fastening) apart, or to take apart the fastenings on (something)I can't unfasten this button. [T]He unfastened his belt and dropped his trousers. [T]This blouse unfastens (= can be unfastened) at the back. [I]
UNFASTEN
Meaning of UNFASTEN in English
Cambridge English vocab. Кембриджский английский словарь. 2012