Mistress
Part of speech: noun
Definition: a woman, specifically one with control, authority or ownership a female teacher a woman who (dishonorably) displaces a wife in the affections of a man; a woman, other than his wife, with whom a married man has a continuing sexual relationship a dominatrix
Madam
Part of speech: noun
Definition: A polite form of address for a woman or lady.The mistress of a household.A conceited or quarrelsome girl.A woman who runs a brothel.
Example sentence: If I can't eat the meal in a restaurant, and the waiter asks, 'Is everything all right, Madam?', I tell them that I'm on a diet.