priestess vs adult female

priestess and adult female both are nouns.

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

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

Other hypernyms of priestess include priest, woman.

priestess (noun)	adult female (noun)
a woman priest	an adult female person (as opposed to a man)