republican vs advocator

republican and advocator both are nouns.

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

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

Other hypernyms of republican include advocate, exponent, proponent.

republican (noun)	advocator (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)	advocator (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