champion vs contender

champion and contender both are nouns.

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

As nouns, contender is a hypernym of champion; that is, contender is a word with a broader meaning than champion:

Other hypernyms of champion include challenger, competition, competitor, rival.

champion (noun)	contender (noun)
someone who fights for a cause	the contestant you hope to defeat
someone who has won first place in a competition
a person who backs a politician or a team etc.
someone who is dazzlingly skilled in any field

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

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