family unit vs marriage

family unit and marriage both are nouns.

Word	Noun	Adjective	Verb	Adverb
family unit	Yes	No	No	No
marriage	Yes	No	No	No

As nouns, marriage is a hyponym of family unit; that is, marriage is a word with a more specific, narrower meaning than family unit:

Other hyponyms of family unit include couple, match, mates, man and wife, married couple.

family unit (noun)	marriage (noun)
primary social group; parents and children	the act of marrying; the nuptial ceremony
	two people who are married to each other
	the state of being a married couple voluntarily joined for life (or until divorce)
	a close and intimate union