What is the meaning of Mistress?

A woman, specifically one with great control, authority or ownership

A female teacher

The other woman in an extramarital relationship, generally including sexual relations

A dominatrix

A woman well skilled in anything, or having the mastery over it

a woman regarded with love and devotion; a sweetheart

A married woman; a wife

The jack in the game of bowls

A female companion to a master (a man with control, authority or ownership)

female equivalent of master

female equivalent of mister

Of a woman: to master; to learn or develop to a high degree of proficiency.

To act or take the role of a mistress.

Source: wiktionary.org