fighter vs grappler

fighter and grappler both are nouns.

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

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

fighter (noun)	grappler (noun)
a high-speed military or naval airplane designed to destroy enemy aircraft in the air	a tool consisting of several hooks for grasping and holding; often thrown with a rope
someone who fights (or is fighting)	combatant who tries to throw opponent to the ground
someone who fights for a cause