The Collaborative International Dictionary of English v.0.48:

Optimistic \Op`ti*mis"tic\, a.
   1. (Metaph.) Of or pertaining to optimism; tending, or
      conforming, to the opinion that all events are ordered for
      the best.
      [1913 Webster]

   2. Hopeful; sanguine; as, an optimistic view.
      [1913 Webster]

WordNet (r) 3.0 (2006):

optimistic
    adj 1: expecting the best in this best of all possible worlds;
           "in an optimistic mood"; "optimistic plans"; "took an
           optimistic view" [ant: pessimistic]
    2: expecting the best; "an affirmative outlook" [syn:
       affirmative, optimistic]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "optimistic":
   Leibnizian, agape, agog, all agog, anticipant, anticipating,
   anticipative, anticipatory, awaiting, beaming, blithe, blithesome,
   bright, bright and sunny, buoyant, certain, cheerful, cheery,
   chiliastic, confident, couleur de rose, eager, elated, eupeptic,
   euphoric, exalted, exhilarated, expectant, expecting, flushed,
   forearmed, forestalling, forewarned, gaping, genial, glad,
   gladsome, glowing, happy, high, hopeful, idealistic,
   in anticipation, in expectation, in good spirits, in high spirits,
   irrepressible, laughing, looking for, looking forward to,
   millenarian, millennialistic, not surprised, of good cheer,
   perfectibilitarian, perfectionist, pleasant, positive, prepared,
   radiant, ready, riant, rose-colored, roseate, rosy, sanguine,
   sanguineous, smiling, sparkling, sunny, sure, unsurprised, upbeat,
   utopian, waiting, waiting for, watching for, winsome