What is a Synonym for mistress?

Depending on context, mistress can have several meanings and therefore several 'opposites' or male equivalents:

Mistress: a woman in position of authority, control, or ownership; male eqivalent = Master

Mistress: a woman skilled in a particular subject or activity; male equivalent = Master

Mistress: a woman having a sexual relationship with a married man; opposite = wife.

Mistress: chiefly Brit. a female schoolteacher; male equivalent = Master

Mistress: archaic Mrs; opposite = Miss; male equivalent = Mister, Mr