Source : Webster's Revised Unabridged Dictionary (1913)

Pessimism \Pes"si*mism\, n. [L. pessimus worst, superl. of pejor
   worse: cf. F. pessimisme. Cf. {Impair}.]
   1. (Metaph.) The opinion or doctrine that everything in
      nature is ordered for or tends to the worst, or that the
      world is wholly evil; -- opposed to {optimism}.

   2. A disposition to take the least hopeful view of things.

Source : WordNet®

pessimism
     n 1: the feeling that things will turn out badly [ant: {optimism}]
     2: a general disposition to look on the dark side and to expect
        the worst in all things [ant: {optimism}]