VERB (3)

1. open the lock of;
- Example: "unlock the door"

2. set free or release;

3. become unlocked;
- Example: "The door unlocked from the inside"

The Collaborative International Dictionary of English v.0.48:

Unlock \Un*lock"\, v. t. [Cf. AS. unl?can. See 1st Un-, and
   Lock, v. t.]
   1. To unfasten, as what is locked; as, to unlock a door or a
      chest.
      [1913 Webster]

   2. To open, in general; to lay open; to undo.
      [1913 Webster]

            Unlock your springs, and open all your shades.
                                                  --Pope.
      [1913 Webster]

            [Lord] unlock the spell of sin.       --J. H.
                                                  Newman.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unlock
    v 1: open the lock of; "unlock the door" [ant: lock]
    2: set free or release
    3: become unlocked; "The door unlocked from the inside" [ant:
       lock]

Moby Thesaurus II by Grady Ward, 1.0:

145 Moby Thesaurus words for "unlock":
   account for, allegorize, answer, bare, bottom, cast off, clarify,
   clear, clear up, crack, debug, decipher, decode, demonstrate,
   demythologize, deobstruct, detach, disclose, disengage,
   disentangle, divine, do, doff, dope, dope out, elucidate,
   enlighten, euhemerize, exemplify, explain, explain away, explicate,
   expose, exposit, expound, fathom, figure out, find out,
   find the answer, find the solution, free, get, get right,
   give reason for, give the meaning, guess, guess right, have it,
   hit it, illuminate, illustrate, interpret, liberate, loose, loosen,
   make clear, make out, make plain, manifest, open the lock, patefy,
   plumb, popularize, psych, psych out, puzzle out, rationalize,
   ravel, ravel out, release, remove, resolve, reveal, riddle,
   shed light upon, show, show how, show the way, simplify, solve,
   sort out, spell out, take off, throw light upon, unbar, unbind,
   unblock, unbolt, unbridle, unbuckle, unbutton, uncage, uncase,
   unchain, unclasp, unclench, unclog, unclutch, uncork, uncover,
   uncurtain, undo, undrape, unfasten, unfetter, unfold, unfoul,
   ungag, unglue, unhandcuff, unhobble, unlace, unlash, unlatch,
   unleash, unloose, unloosen, unmanacle, unmuzzle, unpen, unpinion,
   unplug, unravel, unriddle, unroll, unscramble, unseal, unshackle,
   unsheathe, unshut, unstick, unstop, unstrap, untangle, untether,
   untie, untruss, untwist, unveil, unweave, unwrap, unyoke,
   weigh anchor, work, work out