un·fas·ten /-ˈfæsṇ/
(vt.)解開,放鬆
Un·fas·ten v. t. To loose; to unfix; to unbind; to untie.
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unfasten
v 1: cause to become undone; "unfasten your belt" [ant: fasten]
2: become undone or untied; "The shoelaces unfastened" [ant: fasten]