Sentence examples for a mistress from inspiring English sources

"mistress" is a correct and usable word in written English.
It is usually used as a noun and it has multiple uses and meanings. For example, it can be used to refer to a female who has a sexual relationship with a married man, e.g. "The married man had a mistress on the side." It can also be used to refer to a woman who is in a position of authority or control over someone else, e.g. "The teacher was the mistress of the class."