mis·tress 
/ˈmɪstrəs/ noun
plural mis·tress·es /ˈmɪstrəs/ noun [count] 1 : a woman who has control or power over others: such as a : a woman who has a servant or slave
▪ Servants were required to do the mistress's bidding without question.
b : a woman who owns a pet (such as a dog)
▪ The dog was always obedient to its master and mistress.
c formal : the female head of a household
▪ the master and mistress of the house — compare master 2 : a woman who has control of something
▪ She proved herself (to be) mistress of the situation. 3 : a woman who has a sexual relationship with a married man
▪ a married man who has/keeps a mistress ▪ His wife suspected that the woman she'd seen with him was his mistress. 4 a chiefly Brit, old-fashioned : a female teacher : schoolmistress — see also headmistress
b Mistress — used as a title for the female head of certain British colleges ▪ She was Mistress of Girton (College). 5 Mistress old-fashioned — used as a title before the name of a woman ▪ Mistress Jones
▪ Servants were required to do the mistress's bidding without question.
b : a woman who owns a pet (such as a dog)
▪ The dog was always obedient to its master and mistress.
c formal : the female head of a household
▪ the master and mistress of the house — compare master
▪ She proved herself (to be) mistress of the situation.
▪ a married man who has/keeps a mistress ▪ His wife suspected that the woman she'd seen with him was his mistress.
b Mistress — used as a title for the female head of certain British colleges ▪ She was Mistress of Girton (College).
