The Collaborative International Dictionary of English v.0.48:

Unclasp \Un*clasp"\ ([u^]n*kl[.a]sp"), v. t. [1st pref. un- +
   clasp.]
   To loose the clasp of; to open, as something that is fastened
   with, or as with, a clasp; as, to unclasp a book; to unclasp
   the hands; to unclasp one's heart.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unclasp
    v 1: release from a clasp; "She clasped and unclasped her hands"
         [ant: clasp]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "unclasp":
   cast off, detach, disengage, doff, free, leave go, let go,
   let loose of, liberate, loose, loosen, release, remove, take off,
   unbar, unbind, unbolt, unbuckle, unbutton, unchain, unclutch, undo,
   unfasten, unfetter, unglue, unhand, unlace, unlatch, unleash,
   unlock, unloose, unloosen, unstick, unstrap, untie, weigh anchor