side-wife

plural side-wives · alternative side wife · alternative sidewife

1. A woman who (among others) has the potential to become one's wife, or who is fulfilling the role of one's wife in addition to one's actual wife; a concubine

   A gilly (or sheevin) is a side-wife taken by a man who already has a legal wife.

   2012, Robin Furth, Stephen King's The Dark Tower Concordance

   3 more examples

   If, however, his wife gave him a handmaiden and he had children by her, he was then barred from taking a side-wife (as a concubine was called).

   1903, Sydney Russell Wrightington, Horace Williams Fuller, Arthur Weightman Spencer, The Green Bag - Volume 15

   She was also a 'sidewife'. Nobody talks about it because she is a rich entrepreneur.

   1998, Yūko Nishimura, Gender, Kinship And Property Rights

   For one who has no husband, as well as for one who acts as a side-wife for a person, who has formed a household, or who lives elsewhere and is not enumerated together [with a husband or children on a population register], […]

   2015, Law, State, and Society in Early Imperial China (2 vols)