campaigner vs write-in

campaigner and write-in both are nouns.

Word	Noun	Adjective	Verb	Adverb
campaigner	Yes	No	No	No
write-in	Yes	No	No	No

As nouns, write-in is a hyponym of campaigner; that is, write-in is a word with a more specific, narrower meaning than campaigner:

campaigner: a politician who is running for public office
write-in: a candidate for public office whose name does not appear on the ballot and so must be written on the ballot by the voters

Other hyponyms of campaigner include dark horse, favorite son, running mate, spoiler, stalking-horse, write-in candidate.

campaigner (noun)	write-in (noun)
a politician who is running for public office	a vote cast by writing in the name of a candidate who is not listed on the ballot
	a candidate for public office whose name does not appear on the ballot and so must be written on the ballot by the voters