From Longman Dictionary of Contemporary Englishunfastenun‧fas‧ten /ʌnˈfɑːsən $ -ˈfæsən/ verb [transitive] FASTEN/DO UPto undo something such as a button, belt, rope etc He unfastened the top button of his shirt.► see thesaurus at openTHESAURUSunfasten to open the two sides of a piece of clothing, bag, belt etcIt was hot in the waiting-room, so I unfastened my coat.Please do not unfasten your seat belt while the vehicle is in motion.undo to unfasten clothes or unfasten buttons, zips etc on clothesMy fingers were so cold that I couldn’t undo the buttons.untie to unfasten the knot that fastens shoes, a tie, a scarf etcHe untied his shoes and kicked them off.unbutton to unfasten the buttons on a piece of clothingShe slowly unbuttoned her blouse.unzip to unfasten clothes, bags etc by unfastening a zipShe unzipped the case and took out a thick file.loosen to unfasten clothes a little, but not completely, in order to make yourself more comfortableCarter 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. → See Verb table
Examples from the Corpus
unfasten• He sat her down and began to unfasten her coat.• She watched him unfasten his belt, and drop his trousers.• FitzAlan moved a pace to meet them, his free hand unfastening his cloak.• Jack unfastened his seatbelt and stepped out of the car.• He'd discarded his trousers and was unfastening his shirt when she realised she was staring.• I went up to my room and began unfastening my black skirt.• It was hot in the waiting-room, so I unfastened my coat.• Ripping off her Englishness and casting it aside was as easy as unfastening the collar of her dress.• She flinched once, then started to obey, unfastening the ties at the neck of her gown with shaking fingers.• Do not unfasten your safety belt until the plane has stopped. 