gladiator

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

• noun A person, usually a professional combatant, a captive, or a slave, trained to entertain the public by engaging in mortal combat with another person or a wild animal in the ancient Roman arena.
• noun A person engaged in a controversy or debate, especially in public; a disputant.
• noun Sports A professional boxer.

from The Century Dictionary.

• noun In Rom. antiq., one who fought in public for the entertainment of the people, either with other gladiators or with wild animals.
• noun A combatant in general; a boxer or prize-fighter; a wrestler; also, a disputant.

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

• noun Originally, a swordplayer; hence, one who fought with weapons in public, either on the occasion of a funeral ceremony, or in the arena, for public amusement.
• noun One who engages in any fierce combat or controversy.

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

• noun a person (professional or slave) who entertained the public by engaging in mortal combat with another, or with a wild animal
• noun by extension a disputant in a public controversy or debate
• noun a professional boxer

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

• noun a professional boxer
• noun (ancient Rome) a professional combatant or a captive who entertained the public by engaging in mortal combat