femme fatale vs adult female

femme fatale and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
femme fatale	Yes	No	No	No
adult female	Yes	No	No	No

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

Other hypernyms of femme fatale include woman.

femme fatale (noun)	adult female (noun)
a woman who is considered to be dangerously seductive	an adult female person (as opposed to a man)