Alan Wisdom brings back an old word for an even older concept:
In ancient times, there was an option for a man who desired a regular sex partner but did not wish to marry her. He could take a low-status woman as a concubine. He could enjoy her company as long as it pleased him, and he could dismiss her at any time. The man made no promises and signed no contract; consequently, the concubine had few legal protections. Any children that she bore would have an inferior legal status.
The early Church fought long and hard against concubinage. It insisted that such a sexual relationship, without the permanent and total commitment expressed in marriage vows, was immoral and unjust. Over the course of a thousand years, concubinage retreated into the shadows of social disapproval.
In the past 40 years, it seems, concubinage has come to light again under a different name. Like ancient concubinage, contemporary cohabitation is a deliberately ambiguous relationship. The partners make no promises and have no legal obligations to one another. The arrangement has no specified duration and can be terminated at a moment’s notice. Those who cohabit tend to be of lower social status. Their children, on average, do not fare as well as children born to married couples.
(Via: Gene Veith)