mistress

mistress /ˈmɪstrəs/ noun
plural mistresses
mistress
/ˈmɪstrəs/
noun
plural mistresses
Britannica Dictionary definition of MISTRESS
[count]
1 
: a woman who has control or power over others: such as
a  old-fashioned : a woman who has a servant
b  : a woman who owns a pet (such as a dog)
c  formal : the female head of a household — compare master
2 
: a woman who has control of something
3 
: a woman who has a sexual relationship with a married man
4 
a  chiefly British, old-fashioned : a female teacher : schoolmistress — see also headmistress
b  Mistress — used as a title for the female head of certain British colleges
5 
Mistress old-fashioned — used as a title before the name of a woman