The Collaborative International Dictionary of English v.0.48:

Cowcatcher \Cow"catch`er\ (-k?ch`?r), n.
   A strong inclined frame, usually of wrought-iron bars, in
   front of a locomotive engine, for catching or throwing off
   obstructions on a railway, as cattle; the pilot. [U.S.]

   Syn: fender, buffer, pilot.
        [1913 Webster]

WordNet (r) 3.0 (2006):

cowcatcher
    n 1: an inclined metal frame at the front of a locomotive to
         clear the track [syn: fender, buffer, cowcatcher,
         pilot]