The Collaborative International Dictionary of English v.0.48:

Disconcert \Dis`con*cert"\, v. t. [imp. & p. p. Disconcerted;
   p. pr. & vb. n. Disconcerting.] [Pref. dis- + concert: cf.
   OF. desconcerter, F. d['e]concerter.]
   1. To break up the harmonious progress of; to throw into
      disorder or confusion; as, the emperor disconcerted the
      plans of his enemy.
      [1913 Webster]

   2. To confuse the faculties of; to disturb the composure of;
      to discompose; to abash.
      [1913 Webster]

            The embrace disconcerted the daughter-in-law
            somewhat, as the caresses of old gentlemen unshorn
            and perfumed with tobacco might well do.
                                                  --Thackeray.

   Syn: To discompose; derange; ruffle; confuse; disturb;
        defeat; frustrate.
        [1913 Webster]

WordNet (r) 3.0 (2006):

disconcerted
    adj 1: having self-possession upset; thrown into confusion; "the
           hecklers pelted the discombobulated speaker with anything
           that came to hand"; "looked at each other dumbly, quite
           disconcerted"- G.B.Shaw [syn: discombobulated,
           disconcerted]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "disconcerted":
   abashed, abroad, adrift, afflicted, agitated, all shook up, amiss,
   askew, astray, at sea, awry, baffled, balled-up, beset, bewildered,
   bothered, cast down, chagrined, chaotic, chapfallen, clueless,
   cockeyed, confused, convulsed, deranged, disarranged, discomfited,
   discomforted, discomposed, dislocated, dismayed, disordered,
   disorderly, disorganized, disoriented, disquieted, distracted,
   distraught, distressed, disturbed, embarrassed, fazed, flustered,
   fluttered, fussed, guessing, haywire, hung up, ill at ease,
   in a fix, in a jumble, in a maze, in a pickle, in a pother,
   in a pucker, in a scrape, in a stew, in a sweat, in a swivet,
   in a tizzy, in disorder, jumbled, lost, mazed, misplaced, mixed-up,
   mortified, off the track, on the fritz, out of countenance,
   out of gear, out of joint, out of kelter, out of kilter,
   out of order, out of place, out of tune, out of whack, perplexed,
   perturbed, put off, put out, put-out, put-upon, puzzled, queasy,
   rattled, roily, ruffled, shaken, shook, shuffled, troubled, turbid,
   turbulent, turned around, uncomfortable, uneasy, unsettled, upset,
   without a clue