unpin

from WordNet (r) 3.0 (2006)

unpin
    v 1: remove the pins from; unfasten the pins of [ant: {pin}]

from The Collaborative International Dictionary of English v.0.48

Unpin \Un*pin"\, v. t. [1st pref. un- + pin.]
   To loose from pins; to remove the pins from; to unfasten; as,
   to unpin a frock; to unpin a frame.
   [1913 Webster]