The Collaborative International Dictionary of English v.0.48:

Abase \A*base"\ ([.a]*b[=a]s"), v. t. [imp. & p. p. Abased
   ([.a]*b[=a]st"); p. pr. & vb. n. Abasing.] [F. abaisser,
   LL. abassare, abbassare; ad + bassare, fr. bassus low. See
   Base, a.]
   [1913 Webster]
   1. To lower or depress; to throw or cast down; as, to abase
      the eye. [Archaic] --Bacon.
      [1913 Webster]

            Saying so, he abased his lance.       --Shelton.
      [1913 Webster]

   2. To cast down or reduce low or lower, as in rank, office,
      condition in life, or estimation of worthiness; to
      depress; to humble; to degrade.
      [1913 Webster]

            Whosoever exalteth himself shall be abased. --Luke
                                                  xiv. ll.
      [1913 Webster]

   Syn: To Abase, Debase, Degrade. These words agree in
        the idea of bringing down from a higher to a lower
        state. Abase has reference to a bringing down in
        condition or feelings; as, to abase the proud, to abase
        one's self before God. Debase has reference to the
        bringing down of a thing in purity, or making it base.
        It is, therefore, always used in a bad sense, as, to
        debase the coin of the kingdom, to debase the mind by
        vicious indulgence, to debase one's style by coarse or
        vulgar expressions. Degrade has reference to a bringing
        down from some higher grade or from some standard. Thus,
        a priest is degraded from the clerical office. When used
        in a moral sense, it denotes a bringing down in
        character and just estimation; as, degraded by
        intemperance, a degrading employment, etc. "Art is
        degraded when it is regarded only as a trade."
        [1913 Webster]

WordNet (r) 3.0 (2006):

abase
    v 1: cause to feel shame; hurt the pride of; "He humiliated his
         colleague by criticising him in front of the boss" [syn:
         humiliate, mortify, chagrin, humble, abase]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "abase":
   abash, bring down, bring low, bump, bust, cast down, cower, cringe,
   crush, debase, degrade, demean, demote, deplume, diminish,
   disgrade, displume, downgrade, dump, dump on, fawn, grovel, humble,
   humiliate, lower, put down, reduce, set down, sink, strip of rank,
   take down, toady, trip up, truckle