unmarried woman vs adult female

unmarried woman and adult female both are nouns.

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

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

Other hypernyms of unmarried woman include woman.

unmarried woman (noun)	adult female (noun)
a woman who is not married	an adult female person (as opposed to a man)