The Collaborative International Dictionary of English v.0.48:

Picador \Pic`a*dor"\, n. [Sp.]
   A horseman armed with a lance, who in a bullfight receives
   the first attack of the bull, and excites him by picking him
   without attempting to kill him.
   [1913 Webster]

WordNet (r) 3.0 (2006):

picador
    n 1: the horseman who pricks the bull with a lance early in the
         bullfight to goad the bull and to make it keep its head low