mistress

noun

female who is in a sexual relationship, where the other or both parties to the relationship are also in another committed relationship (usually marriage)

Wiktionary

Pronunciation: /ˈmɪs.tɹɪs/ / /ˈmɪs.ʈrɪs/ / /mɪsˈʈrɛs/

noun

Used as the title of a married woman before her name. Now used only in the abbreviated form Mrs.
“The sound of Mistress Affery cautiously chaining the door before she opened it, caused them both to look that way.”
“Mistress Cordelia Carfax shivered and gathered her silk shawl about her shoulders. […] Any shows of affection Mistress Carfax did display were usually reserved for her pedigree pug.”
Used as the title of a female dominant.

verb

Etymology: Etymology tree Proto-Indo-European *meǵh₂-der.? Proto-Indo-European *meh₂-der.? Proto-Italic *magisteros Latin magister, magistrum Old French maistre Ancient Greek -ισσα (-issa)bor. Latin -issader. Old French -esse Old French maistressebor. Middle English maistresse English mistress From Middle English maistresse, from Old French maistresse (whence French maîtresse), feminine of maistre (“master”). By surface analysis, mist(e)r + -ess.

Of a woman: to master; to learn or develop to a high degree of proficiency.
“These films give a glimpse of women on the way to mistressing their own destiny.”
To act or take the role of a mistress.
“[…] housewifery, maternity, charity, the life conventual, the chatter of a court, the mistressing of a great house […]”