mistress

[mis-tris] /ˈmɪs trɪs/
noun
1.
a woman who has authority, control, or power, especially the female head of a household, institution, or other establishment.
2.
a woman employing, or in authority over, servants or attendants.
3.
a female owner of an animal, or formerly, a slave.
4.
a woman who has the power of controlling or disposing of something at her own pleasure:
mistress of a great fortune.
5.
(sometimes initial capital letter) something regarded as feminine that has control or supremacy:
Great Britain, the mistress of the seas.
6.
a women who is skilled in something, as an occupation or art.
7.
a woman who has a continuing, extramarital sexual relationship with one man, especially a man who, in return for an exclusive and continuing liaison, provides her with financial support.
8.
British. a female schoolteacher; schoolmistress.
9.
(initial capital letter) a term of address in former use and corresponding to Mrs., Miss, or Ms.
10.
Archaic. sweetheart.
Origin
1275-1325; Middle English maistresse < Middle French, Old French, equivalent to maistre master + -esse -ess
Related forms
mistressed, adjective
mistress-ship, noun
Usage note
See -ess.
British Dictionary definitions for mistress

mistress

/ˈmɪstrɪs/
noun
1.
a woman who has a continuing extramarital sexual relationship with a man
2.
a woman in a position of authority, ownership, or control, such as the head of a household
3.
a woman or female personification having control over something specified: she was mistress of her own destiny
4.
(mainly Brit) short for schoolmistress
5.
an archaic or dialect word for sweetheart
Word Origin
C14: from Old French; see master, -ess

Mistress

/ˈmɪstrɪs/
noun
1.
an archaic or dialect title equivalent to Mrs
Word Origin and History for mistress
n.

early 14c., "female teacher, governess," from Old French maistresse "mistress (lover); housekeeper; governess, female teacher" (Modern French maîtresse), fem. of maistre "master" (see master (n.)). Sense of "a woman who employs others or has authority over servants" is from early 15c. Sense of "kept woman of a married man" is from early 15c.