athlete

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One who participates in physical exercise or sports, especially in competitive events.
• noun One possessing the requisite strength, agility, and endurance for success in sports.

from The Century Dictionary.

• noun In Greek antiquity, one who contended for a prize in the public games.
• noun Hence—2. Any one trained to exercises of agility and strength; one accomplished in athletics; a man full of strength and activity.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Antiq.) One who contended for a prize in the public games of ancient Greece or Rome.
• noun Any one trained to contend in exercises requiring great physical agility and strength; one who has great activity and strength; a champion.
• noun One fitted for, or skilled in, intellectual contests.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A participant in a group of sporting activities which includes track and field, road running, cross country running and racewalking.
• noun US A person who actively participates in physical sports, possibly highly skilled in sports. (Known in British English as a "sportsperson".)
• noun An exceptionally physically fit person.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a person trained to compete in sports