“+ transitive verb
Etymology: Middle English unfastnen, from un- (II) + fastnen to fasten
: to make loose:
a. obsolete : make less firm : weaken
unfasten his resolutions — Thomas Carte
b. : unpin , unbuckle
unfasten the bolt of a door
unfasten a belt
c. : undo
unfasten the buttons of a dress
d. : detach
unfasten a boat from its moorings
e. : untie
unfastened the string and opened the package