battler vs boxer

battler and boxer both are nouns.

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

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

battler (noun)	boxer (noun)
someone who fights (or is fighting)	a breed of stocky medium-sized short-haired dog with a brindled coat and square-jawed muzzle developed in Germany
	someone who fights with his fists for sport
	a workman employed to pack things into containers