The Collaborative International Dictionary of English v.0.48:

Racer \Ra"cer\ (r[=a]"s[~e]r), n.
   1. One who, or that which, races, or contends in a race;
      esp., a race horse.
      [1913 Webster]

            And bade the nimblest racer seize the prize. --Pope.
      [1913 Webster]

   2. (Zool.) The common American black snake.
      [1913 Webster]

   3. (Mil.) One of the circular iron or steel rails on which
      the chassis of a heavy gun is turned.
      [1913 Webster]

WordNet (r) 3.0 (2006):

racer
    n 1: someone who drives racing cars at high speeds [syn:
         racer, race driver, automobile driver]
    2: a fast car that competes in races [syn: racer, race car,
       racing car]
    3: an animal that races
    4: slender fast-moving North American snakes

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "racer":
   Jehu, amateur athlete, archer, athlete, ballplayer, baseballer,
   baseman, batter, battery, blocking back, bowman, catcher, center,
   coach, competitor, cricketer, defensive lineman, end, entry,
   favorite, flier, footballer, games-player, gamester, goer, guard,
   hell-driver, horse racer, hummer, hustler, infielder, jock, jockey,
   jumper, lineman, mudder, offensive lineman, outfield, outfielder,
   plate horse, plater, player, pole horse, poloist, pony,
   professional athlete, pugilist, quarterback, race horse, runner,
   scorcher, sizzler, skater, speed demon, speeder, sport, sportsman,
   stable, stake horse, staker, starter, steeplechaser, stepper,
   string, tackle, tailback, toxophilite, turfman, wingback,
   wrestler



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

RACER
       Renamed Abox and Concept Expression Reasoner