n.1 a female head of a household.
2 a a woman in authority over others. b the female owner of a pet.
3 a woman with power to control etc. (often foll. by of: mistress of the situation).
4 Brit. a a female teacher (music mistress). b a female head of a college etc.
5 a a woman (other than his wife) with whom a married man has a (usu. prolonged) sexual relationship. b archaic or poet. a woman loved and courted by a man.
6 archaic or dial. (as a title) MRS.
Phrases and idioms:
Mistress of the Robes a lady in charge of the Queen's wardrobe.
Etymology: ME f. OF maistresse f. maistre MASTER