1
general::
unfasten
to open the two sides of a piece of clothing, bag, belt etc:
• It was hot in the waiting-room, so I unfastened my coat. • Please do not unfasten your seatbelt while the vehicle is in motion.
undo
to unfasten clothes or unfasten buttons, zips etc on clothes:
• My fingers were so cold that I couldn’t undo the buttons.
untie
to unfasten the knot that fastens shoes, a tie, a scarf etc:
• He untied his shoes and kicked them off.
unbutton
to unfasten the buttons on a piece of clothing:
• She slowly unbuttoned her blouse.
unzip
to unfasten clothes, bags etc by unfastening a zip:
• She unzipped the case and took out a thick file.
loosen
to unfasten clothes a little, but not completely, in order to make yourself more comfortable:
• Carter took off his jacket and loosened his tie.
open
to unfasten a bag, box, or other container:
• ‘Could you open your bag, please?’ said the security guard.
Longman-Thesaurus