kept man vs adult female

kept man and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
kept man	Yes	No	No	No
adult female	Yes	No	No	No

As nouns, adult female is a hypernym of kept man; that is, adult female is a word with a broader meaning than kept man:

kept man: an adulterous man; a man who has an ongoing extramarital sexual relationship with a woman
adult female: an adult female person (as opposed to a man)

Other hypernyms of kept man include woman.

kept man (noun)	adult female (noun)
an adulterous man; a man who has an ongoing extramarital sexual relationship with a woman	an adult female person (as opposed to a man)