boxer vs fighter

boxer and fighter both are nouns.

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

As nouns, fighter is a hypernym of boxer; that is, fighter is a word with a broader meaning than boxer:

Other hypernyms of boxer include battler, belligerent, combatant, scrapper.

boxer (noun)	fighter (noun)
a breed of stocky medium-sized short-haired dog with a brindled coat and square-jawed muzzle developed in Germany	a high-speed military or naval airplane designed to destroy enemy aircraft in the air
someone who fights with his fists for sport	someone who fights (or is fighting)
a workman employed to pack things into containers	someone who fights for a cause