rival vs champ

rival and champ both are nouns.

Word	Noun	Adjective	Verb	Adverb
rival	Yes	Yes	Yes	No
champ	Yes	No	Yes	No

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

rival (noun)	champ (noun)
the contestant you hope to defeat	someone who has won first place in a competition

rival (adjective)	champ (adjective)
as a rival in a competition

rival (verb)	champ (verb)
be the rival of, be in competition with	chew noisily or vigorously
be equal to in quality or ability	chafe at the bit, like horses