The Collaborative International Dictionary of English v.0.48:

Pessimist \Pes"si*mist\, Pessimistic \Pes`si*mis"tic\, a.
   (Metaph.)
   Of or pertaining to pessimism; characterized by pessimism;
   gloomy; foreboding. "Giving utterance to pessimistic doubt."
   --Encyc. Brit.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pessimistic
    adj 1: expecting the worst possible outcome [ant: optimistic]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "pessimistic":
   Cassandra-like, Cassandran, Cassandrian, bleak, blue, bowed-down,
   cast down, cheerless, cynical, dashed, defeatist, dejected,
   depressed, despairing, despondent, desponding, discouraged,
   disheartened, dismal, dispirited, down, downbeat, downcast,
   downhearted, drooping, droopy, feeling low, forlorn, gloomy, glum,
   heartless, hopeless, hypochondriac, hypochondriacal,
   in low spirits, in the depths, in the doldrums, in the dumps,
   inauspicious, joyless, languishing, low, low-spirited, melancholy,
   negative, negativistic, nihilistic, pessimist, pining, sad,
   spiritless, subdued, suicidal, uncheerful, unhappy, weary of life,
   woebegone, world-weary