The Collaborative International Dictionary of English v.0.48:
pacesetter \pacesetter\ n. A horse used to set the pace in racing. Syn: pacer, pacemaker. [WordNet 1.5]WordNet (r) 3.0 (2006):
pacesetter n 1: a leading instance in its field; "the new policy will be a pacesetter in community relations" [syn: pacesetter, pacemaker] 2: a horse used to set the pace in racing [syn: pacer, pacemaker, pacesetter]