Racer \Ra"cer\, n.

1. One who, or that which, races, or contends in a race; esp., a race horse.

And bade the nimblest racer seize the prize. --Pope.

2. (Zo["o]l.) The common American black snake.

3. (Mil.) One of the circular iron or steel rails on which the chassis of a heavy gun is turned.

Source: Webster's Revised Unabridged Dictionary (1913)