The Collaborative International Dictionary of English v.0.48:

Unlatch \Un*latch"\, v. i. [imp. & p. p. Unlatched; p. pr. &
   vb. n. Unlatching.] [1st un- + latch.]
   To open or loose by lifting the latch; as, to unlatch a door.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "unlatch":
   bare, cast off, clear, deobstruct, detach, disclose, disengage,
   doff, expose, free, liberate, loose, loosen, manifest, patefy,
   release, remove, reveal, take off, 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, unleash, unlock, unloose,
   unloosen, unmanacle, unmuzzle, unpen, unpinion, unplug, unroll,
   unseal, unshackle, unsheathe, unshut, unstick, unstop, unstrap,
   untether, untie, untruss, unveil, unwrap, unyoke, weigh anchor