Source : Webster's Revised Unabridged Dictionary (1913)

Optimist \Op"ti*mist\, n. [Cf. F. optimiste.]
   1. (Metaph.) One who holds the opinion that all events are
      ordered for the best.

   2. One who looks on the bright side of things, or takes
      hopeful views; -- opposed to {pessimist}.

Source : WordNet®

optimist
     n : a person disposed to take a favorable view of things [ant: {pessimist}]