The Collaborative International Dictionary of English v.0.48:

Disillusionment \Dis`il*lu"sion*ment\, n.
   The act of freeing from an illusion, or the state of being
   freed therefrom.
   [1913 Webster]

WordNet (r) 3.0 (2006):

disillusionment
    n 1: freeing from false belief or illusions [syn:
         disenchantment, disillusion, disillusionment]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "disillusionment":
   bafflement, balk, ban, betrayed hope, blackball, blackballing,
   blasted expectation, blighted hope, blow, buffet, comedown,
   complaint, cruel disappointment, dash, dashed hope, defeat,
   dim view, disagreement, disappointment, disapprobation,
   disapproval, discomfiture, discontent, discontentedness,
   discontentment, disenchantment, disesteem, disfavor,
   disgruntlement, disillusion, displeasure, disrespect,
   dissatisfaction, dissent, distaste, exclusion, failure,
   fallen countenance, fiasco, fizzle, foiling, forlorn hope,
   frustration, hope deferred, indignation, letdown, low estimation,
   low opinion, mirage, objection, opposition, opposure, ostracism,
   protest, rejection, setback, sore disappointment, tantalization,
   tease, thumbs-down, unhappiness