Pacer

['peɪsə] or ['pesɚ]

(noun.) a horse trained to a special gait in which both feet on one side leave the ground together.

(noun.) a horse used to set the pace in racing.

Checked by Horatio--From WordNet

(n.) One who, or that which, paces; especially, a horse that paces.

Checker: Marge

Checked by Blanchard