republican vs proponent

republican and proponent both are nouns.

Word	Noun	Adjective	Verb	Adverb
republican	Yes	Yes	No	No
proponent	Yes	No	No	No

As nouns, proponent is a hypernym of republican; that is, proponent is a word with a broader meaning than republican:

Other hypernyms of republican include advocate, advocator, exponent.

republican (noun)	proponent (noun)
an advocate of a republic (usually in opposition to a monarchy)	a person who pleads for a cause or propounds an idea

republican (adjective)	proponent (adjective)
relating to or belonging to the Republican Party
having the supreme power lying in the body of citizens entitled to vote for officers and representatives responsible to them or characteristic of such government