A woman who lives with a man, but who is not a wife.
A slave-girl or woman, kept for instance in a harem, who is held for sexual service.
A sexual partner, especially a woman, to whom one is not or cannot be married.
A married woman; a wife
The other woman in an extramarital relationship, generally including sexual relations
A female companion to a master (a man with control, authority or ownership)
A woman, specifically one with great control, authority or ownership
a woman regarded with love and devotion; a sweetheart
A female teacher
A dominatrix
A woman well skilled in anything, or having the mastery over it
To act or take the role of a mistress.
Of a woman: to master; to learn or develop to a high degree of proficiency.