nanny vs adult female

nanny and adult female both are nouns.

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

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

Other hypernyms of nanny include keeper, woman.

nanny (noun)	adult female (noun)
female goat	an adult female person (as opposed to a man)
a woman who is the custodian of children