Home › Words › U › unfastunfastunfast means to loose; release.Among words judged in Lexicurio's Arena, unfast ranks #2,160 of 42,762 for Qualifying.EtymologyFrom Middle English unfasten, unvesten, onfesten, equivalent to un- + fast.verbTo loose; release.adjNot fast or safe; not secure.Definitions & examples from Wiktionary (CC BY-SA 3.0).