pacer

A horse trained to pace.

One who paces, or measures by pacing.

A horse whose natural gait is a pace.

Hence, a fast horse; by extension, anything that exhibits remarkable speed or activity.

Same as pace-maker, 1.

One who, or that which, paces.

A horse trained to a special gait in which both feet on one side leave the ground together; a horse that paces.

A horse used to set the pace in racing.

One who paces.