Mistress
/ˈmɪstɹɪs/
noun
A woman, specifically one with great control, authority or ownership
“(male equivalent) master”
A female teacher
“(male equivalent) master”
The other woman in an extramarital relationship, generally including sexual relations
Synonyms: bit on the side, comaré, fancy woman, goomah, boss, head, leader, schoolmarm
verb
Of a woman: to master; to learn or develop to a high degree of proficiency.
To act or take the role of a mistress.