concubinage vs cohabitation

concubinage and cohabitation both are nouns.

Word	Noun	Adjective	Verb	Adverb
concubinage	Yes	No	No	No
cohabitation	Yes	No	No	No

As nouns, cohabitation is a hypernym of concubinage; that is, cohabitation is a word with a broader meaning than concubinage:

concubinage: cohabitation without being legally married
cohabitation: the act of living together and having a sexual relationship (especially without being married)

concubinage (noun)	cohabitation (noun)
cohabitation without being legally married	the act of living together and having a sexual relationship (especially without being married)