courtesan vs kept woman

courtesan and kept woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
courtesan	Yes	No	No	No
kept woman	Yes	No	No	No

As nouns, kept woman is a hypernym of courtesan; that is, kept woman is a word with a broader meaning than courtesan:

courtesan: a woman who cohabits with an important man
kept woman: an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man

Other hypernyms of courtesan include fancy woman, mistress.

courtesan (noun)	kept woman (noun)
a woman who cohabits with an important man	an adulterous woman; a woman who has an ongoing extramarital sexual relationship with a man