The Collaborative International Dictionary of English v.0.48:

vamoose \va*moose"\ (v[a^]*m[=oo]s"), v. i. & t. [Sp. vamos let
   us go.]
   To depart quickly; to depart from. [Written also vamos, and
   vamose.] [Slang, Eng. & U. S.]
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

vamose \va*mose"\ (v[.a]*m[=o]s"), v. i. & t. [Sp. vamos let us
   go.]
   To vamoose; -- an older spelling and pronunciation variant.
   [Written also vamos, and vamoose.] [Slang, Eng. & U. S.]
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

vamoose
    v 1: leave suddenly; "She persuaded him to decamp"; "skip town"
         [syn: decamp, skip, vamoose]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "vamoose":
   be off, beat it, begone, blow, clear out, decamp, dog it,
   duck and run, duck out, flake off, get, get going, get lost,
   get out, git, hightail, hit the road, kite, lam,
   make yourself scarce, scram, shove off, skedaddle, skin out, split,
   take a powder, take off