The Collaborative International Dictionary of English v.0.48:

Bearish \Bear"ish\, a.
   1. Partaking of the qualities of a bear; resembling a bear in
      temper or manners. --Harris.
      [1913 Webster]

   2. (Stock market) Fearful of or anticipating falling prices,
      as in the stock market; as, bearish sentiment inhibited
      buying.
      [PJC]

   3. (Stock market) Tending to cause prices to fall. "bearish
      news about inflation caused a sharp drop in the Dow."
      [PJC]

   4. Hence: Pessimistic.
      [PJC]

WordNet (r) 3.0 (2006):

bearish
    adj 1: expecting prices to fall