The Collaborative International Dictionary of English v.0.48:

Frustrate \Frus"trate\, v. t. [imp. & p. p. Frustrated; p. pr.
   & vb. n. Frustrating.]
   1. To bring to nothing; to prevent from attaining a purpose;
      to disappoint; to defeat; to baffle; as, to frustrate a
      plan, design, or attempt; to frustrate the will or
      purpose.
      [1913 Webster]

            Shall the adversary thus obtain
            His end and frustrate thine ?         --Milton.
      [1913 Webster]

   2. To make null; to nullifly; to render invalid or of no
      effect; as, to frustrate a conveyance or deed.

   Syn: To balk; thwart; foil; baffle; defeat.
        [1913 Webster]

WordNet (r) 3.0 (2006):

frustrated
    adj 1: disappointingly unsuccessful; "disappointed expectations
           and thwarted ambitions"; "their foiled attempt to capture
           Calais"; "many frustrated poets end as pipe-smoking
           teachers"; "his best efforts were thwarted" [syn:
           defeated, disappointed, discomfited, foiled,
           frustrated, thwarted]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "frustrated":
   asexual, baffled, balked, betrayed, bilked, blasted, blighted,
   castrated, chapfallen, cold, crestfallen, crossed, crushed, dashed,
   defeated, disappointed, dished, disillusioned, dissatisfied,
   emasculated, eunuchized, foiled, frigid, ill done-by, ill-served,
   impotent, let down, neuter, neutral, out of countenance, regretful,
   sexless, sorely disappointed, soured, thwarted, unsexed,
   unsexual