mistress

Universal Words noun 1 a man's (usually a married man's) mistress is a woman that he is having a regular sexual relationship with and who is not his wife 2 (BrE, becoming old-fashioned) a female teacher in a school, especially a private school: the Biology mistress 3 (in the past) the female head of a house, especially one who employed servants: the mistress of the house * Lizzie, fetch your mistress her shawl. 4 the female owner of a dog or other animal 5 (formal) a woman who is in a position of authority or control, or who is highly skilled in sth: She wants to be mistress of her own affairs (= to organize her own life). * She is the mistress of plain speech. compareMASTER