The Collaborative International Dictionary of English v.0.48:

Abash \A*bash"\ ([.a]*b[a^]sh"), v. t. [imp. & p. p. Abashed
   ([.a]*b[a^]sht"); p. pr. & vb. n. Abashing.] [OE. abaissen,
   abaisshen, abashen, OF. esbahir, F. ['e]bahir, to astonish,
   fr. L. ex + the interjection bah, expressing astonishment. In
   OE. somewhat confused with abase. Cf. Finish.]
   To destroy the self-possession of; to confuse or confound, as
   by exciting suddenly a consciousness of guilt, mistake, or
   inferiority; to put to shame; to disconcert; to discomfit.
   [1913 Webster]

         Abashed, the devil stood,
         And felt how awful goodness is.          --Milton.
   [1913 Webster]

         He was a man whom no check could abash.  --Macaulay.
   [1913 Webster]

   Syn: To confuse; confound; disconcert; shame.

   Usage: To Abash, Confuse, Confound. Abash is a stronger
          word than confuse, but not so strong as confound. We
          are abashed when struck either with sudden shame or
          with a humbling sense of inferiority; as, Peter was
          abashed by the look of his Master. So a modest youth
          is abashed in the presence of those who are greatly
          his superiors. We are confused when, from some
          unexpected or startling occurrence, we lose clearness
          of thought and self-possession. Thus, a witness is
          often confused by a severe cross-examination; a timid
          person is apt to be confused in entering a room full
          of strangers. We are confounded when our minds are
          overwhelmed, as it were, by something wholly
          unexpected, amazing, dreadful, etc., so that we have
          nothing to say. Thus, a criminal is usually confounded
          at the discovery of his guilt.
          [1913 Webster]

                Satan stood
                Awhile as mute, confounded what to say.
                                                  --Milton.
          [1913 Webster]

WordNet (r) 3.0 (2006):

abash
    v 1: cause to be embarrassed; cause to feel self-conscious [syn:
         embarrass, abash]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "abash":
   abase, appall, astound, bewilder, bother, bring down, bring low,
   cast down, chagrin, confound, confuse, crush, debase, degrade,
   demean, diminish, discomfit, discompose, disconcert,
   discountenance, dismay, disturb, dump, dump on, embarrass, faze,
   flummox, humble, humiliate, lower, moider, mortify, perturb,
   pother, put down, put out, rattle, reduce, set down, take aback,
   take down, throw into confusion, trip up, upset