fasten UK /ˈfɑːsn̩/US /ˈfæsn̩/verb 2forms 5phrases 2 verb2 •To attach or connect in a secure manner.The sailor fastened the boat to the dock with a half-hitch.Fasten your seat belts! •To cause to take close effect; to make to tell; to land.if I can fasten but one cup upon him — 1603 formsfastened · fastening · fasteneth · fastens · fastenest Phrases with fasten fasten downTo secure something so that it will not be moved away. fasten upTo fasten or attach