unfasten
verb
ʌnˈfɑːsən
verb
1
to
undo
something
such
as
a
button,
belt,
rope
etc
解开〔纽扣、带子、绳子等〕
He
unfastened
the
top
button
of
his
shirt.
他解开了衬衫最上面的那颗扣子。