（被包养的）姘妇/面首
someone who does not work but is instead given money and a place to live by the person she or he is having a sexual relationship with
If he'd married her, he would have become a kept man.
She had no desire to be a kept woman in a loveless marriage.
She was living as the kept woman of a rich painter.
The novel was about a kept woman who left her lover and made a life for herself in the countryside.
See also: kept adjective