The Collaborative International Dictionary of English v.0.48:

Athlete \Ath"lete\, n. [L. athleta, Gr. ? prizefighter, fr. ? to
   contend for a prize, ?, Hom. ?, contest, ? prize; fr. the
   same root as E. wed: cf. F. athl[`e]te.]
   1. (Antiq.) One who contended for a prize in the public games
      of ancient Greece or Rome.
      [1913 Webster]

   2. Any one trained to contend in exercises requiring great
      physical agility and strength; one who has great activity
      and strength; a champion.
      [1913 Webster]

   3. One fitted for, or skilled in, intellectual contests; as,
      athletes of debate.
      [1913 Webster]

WordNet (r) 3.0 (2006):

athlete
    n 1: a person trained to compete in sports [syn: athlete,
         jock]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "athlete":
   amateur athlete, archer, ballplayer, baseballer, baseman, batter,
   battery, blocking back, bowman, catcher, center, coach, competitor,
   cricketer, defensive lineman, end, footballer, games-player,
   gamester, guard, infielder, jock, jumper, lineman,
   offensive lineman, outfield, outfielder, player, poloist,
   professional athlete, pugilist, quarterback, racer, skater, sport,
   sportsman, tackle, tailback, toxophilite, wingback, wrestler