The Collaborative International Dictionary of English v.0.48:

Unstick \Un*stick"\, v. t. [1st pref. un- + stick.]
   To release, as one thing stuck to another. --Richardson.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "unstick":
   cast off, detach, diffuse, disengage, disjoin, disperse, doff,
   ease, ease off, free, let go, let up, liberate, loose, loosen,
   relax, release, remove, scatter, slack, slack off, slacken,
   take off, unbar, unbind, unbolt, unbuckle, unbutton, unchain,
   unclasp, undo, unfasten, unfetter, unglue, unlace, unlatch,
   unleash, unlock, unloose, unloosen, unstrap, untie, weigh anchor