boxer vs gladiator

boxer and gladiator both are nouns.

Word	Noun	Adjective	Verb	Adverb
boxer	Yes	No	No	No
gladiator	Yes	No	No	No

As nouns, gladiator is a hyponym of boxer; that is, gladiator is a word with a more specific, narrower meaning than boxer:

boxer (noun)	gladiator (noun)
a breed of stocky medium-sized short-haired dog with a brindled coat and square-jawed muzzle developed in Germany	(ancient Rome) a professional combatant or a captive who entertained the public by engaging in mortal combat
someone who fights with his fists for sport	a professional boxer
a workman employed to pack things into containers