The Collaborative International Dictionary of English v.0.48:

Disappointed \Dis`ap*point"ed\, a.
   1. Defeated of expectation or hope; balked; as, a
      disappointed person or hope.
      [1913 Webster]

   2. Unprepared; unequipped. [Obs.]
      [1913 Webster]

            Cut off even in the blossoms of my sin,
            Unhouseled, disappointed, unaneled.   --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

disappointed
    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:

100 Moby Thesaurus words for "disappointed":
   against, baffled, balked, beefing, bellyaching, betrayed, bilked,
   bitching, blase, blasted, blighted, chapfallen, complaining,
   complaintful, con, crabbing, crabby, cranky, crestfallen, croaking,
   crossed, crushed, dashed, defeated, dejected, disabused,
   disapprobatory, disapproving, discontented, discouraged,
   disenchanted, disgruntled, disheartened, dished, disillusioned,
   displeased, dissatisfied, dissenting, downcast, downhearted,
   enlightened, envious, failed, faultfinding, foiled, frustrated,
   griping, grouchy, grousing, growling, grumbling, ill done-by,
   ill-served, indignant, let down, low, malcontent, malcontented,
   murmuring, muttering, opposed, opposing, out of countenance,
   out of humor, peevish, petulant, poor, put straight, querulant,
   querulous, rebellious, regretful, resentful, restive, restless,
   robbed of illusion, saddened, set right, sophisticated,
   sorely disappointed, soured, sulky, thwarted, turned-off,
   unaccepting, unaccommodating, unappreciative, unapproving,
   uncharmed, uncomplimentary, undeceived, undone, uneasy,
   unfavorable, unfulfilled, ungratified, unhappy, unsatisfied,
   unspelled, whiny