The Collaborative International Dictionary of English v.0.48:

Trotter \Trot"ter\, n.
   1. One that trots; especially, a horse trained to be driven
      in trotting matches.
      [1913 Webster]

   2. The foot of an animal, especially that of a sheep; also,
      humorously, the human foot.
      [1913 Webster]

WordNet (r) 3.0 (2006):

trotter
    n 1: foot of a pig or sheep especially one used as food
    2: a horse trained to trot; especially a horse trained for
       harness racing [syn: trotting horse, trotter]