The Collaborative International Dictionary of English v.0.48:

Unbolt \Un*bolt"\, v. t. [1st pref. un- + bolt.]
   To remove a bolt from; to unfasten; to unbar; to open. "He
   shall unbolt the gates." --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Unbolt \Un*bolt"\, v. i.
   To explain or unfold a matter; to make a revelation. [Obs.]
   "I will unbolt to you." --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unbolt
    v 1: undo the bolt of; "unbolt the door" [ant: bolt]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "unbolt":
   cast off, detach, disengage, doff, free, liberate, loose, loosen,
   release, remove, take off, unbar, unbind, 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