noblewoman vs adult female

noblewoman and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
noblewoman	Yes	No	No	No
adult female	Yes	No	No	No

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

Other hypernyms of noblewoman include female aristocrat, woman.

noblewoman (noun)	adult female (noun)
a woman of the peerage in Britain	an adult female person (as opposed to a man)