The Collaborative International Dictionary of English v.0.48:

Unbind \Un*bind"\ ([u^]n*b[imac]nd"), v. t. [imp. & p. p.
   Unbound ([u^]n*bound"); p. pr. & vb. n. Unbinding.] [AS.
   unbindan. See Un-, and Bind.]
   To remove a band from; to set free from shackles or
   fastenings; to untie; to unfasten; to loose; as, unbind your
   fillets; to unbind a prisoner's arms; to unbind a load.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unbind
    v 1: untie or unfasten; "unbind the feet of this poor woman"
         [ant: bind]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "unbind":
   cast off, detach, discharge, disengage, doff, emancipate, free,
   liberate, loose, loosen, manumit, release, remove, take off, unbar,
   unbolt, unbridle, unbuckle, unbutton, uncage, unchain, unclasp,
   undo, unfasten, unfetter, ungag, unglue, unhandcuff, unhobble,
   unlace, unlash, unlatch, unleash, unlock, unloose, unloosen,
   unmanacle, unmuzzle, unpen, unpinion, unshackle, unstick, unstrap,
   untether, untie, untruss, unyoke, weigh anchor