to open or make loose; untie, unlock, undo, etc.
to become unfastened
verbun·fas·tened, un·fas·ten·ing, un·fas·tens
To separate the connected parts of.
To become loosened or separated.
(third-person singular simple present unfastens, present participle unfastening, simple past and past participle unfastened)
un- +"Ž fasten