"one who contests, a disputant, a litigant," 1660s, from contestant (adj.), 1660s, from French contestant, present participle of contester (see contest (v.)). Revived and popularized 1861, when it became a journalist's term for the combatants on either side in the U.S. Civil War.
Until mid-18c. usually in Latin form. In this sense, Old English had plegmann "play-man." Meaning "Anyone trained in exercises of agility and strength" is from 1827. Athlete's foot first recorded 1928, for an ailment that has been around much longer.
Middle English pleiere, from Old English plegere "one who takes part in pastimes or amusements," an agent noun from play (v.). The stage senses of "performer of plays, professional actor," also "one who performs on a musical instrument" are from c. 1400. The meaning "contestant in field or martial games" is from early 15c.; of table games, late 14c. As a pimp's word for himself (also playa), it is attested from 1974 (the sexual senses of play (v.) go back to 13c.). Player-piano is attested from 1901.
Friends, who on a domestic stage allot parts to each other, and repeat a drama, are actors, but not players. Many a libertine has taken to the stage for a maintenance, and has become a player without becoming an actor. The great theatres engage those who act well ; the strolling companies those who play cheap. [William Taylor, "English Synonyms Discriminated," 1813]