unfasten
verb [ I or T ] uk/ʌnˈfɑː.sən/ us/ʌnˈfæs.sən/
解开;松开;打开
to release or open something that is fixed or closed
I can't unfasten this button/belt. 我解不开这个扣子／带子。
This blouse unfastens (= can be unfastened) at the back. 这件上衣是从背后解扣的。