gay woman vs adult female

gay woman and adult female both are nouns.

Word	Noun	Adjective	Verb	Adverb
gay woman	Yes	No	No	No
adult female	Yes	No	No	No

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

Other hypernyms of gay woman include gay, homo, homophile, homosexual, woman.

gay woman (noun)	adult female (noun)
a female homosexual	an adult female person (as opposed to a man)