champion vs fighter

champion and fighter both are nouns.

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

As nouns, champion and fighter are synonyms defined as:

Other synonyms of champion include hero, paladin.

champion (noun)	fighter (noun)
someone who fights for a cause	a high-speed military or naval airplane designed to destroy enemy aircraft in the air
someone who has won first place in a competition	someone who fights (or is fighting)
a person who backs a politician or a team etc.	someone who fights for a cause
someone who is dazzlingly skilled in any field

champion (adjective)	fighter (adjective)
holding first place in a contest

champion (verb)	fighter (verb)
protect or fight for as a champion