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]