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]