CONCUBINAGE
concubinage
(noun) cohabitation without being legally married
Source: WordNet® 3.1
Etymology
Noun
concubinage (countable and uncountable, plural concubinages)
The state of cohabiting or living together as man and wife while not married.
The state of being or keeping a concubine.
Source: Wiktionary
Con*cu"bi*nage, n.
1. The cohabiting of a man and a woman who are not legally married;
the state of being a concubine.
Note: In some countries, concubinage is marriage of an inferior kind,
or performed with less solemnity than a true or formal marriage; or
marriage with a woman of inferior condition, to whom the husband does
not convey his rank or quality. Under Roman law, it was the living of
a man and woman in sexual relations without marriage, but in
conformity with local law.
2. (Law)
Definition: A plea, in which it is alleged that the woman suing for dower
was not lawfully married to the man in whose lands she seeks to be
endowed, but that she was his concubine.
Source: Webster’s Unabridged Dictionary 1913 Edition