citizen vs civilian

citizen and civilian both are nouns.

Word	Noun	Adjective	Verb	Adverb
citizen	Yes	No	No	No
civilian	Yes	Yes	No	No

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

citizen: a native or naturalized member of a state or other political community
civilian: a nonmilitary citizen

Other hyponyms of citizen include active citizen, freeperson, private citizen, repatriate, thane, elector, voter.

citizen (noun)	civilian (noun)
a native or naturalized member of a state or other political community	a nonmilitary citizen

citizen (adjective)	civilian (adjective)
	associated with civil life or performed by persons who are not active members of the military