selectwoman vs adult female

selectwoman and adult female both are nouns.

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

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

selectwoman: a female elected member of a board of officials who run New England towns
adult female: an adult female person (as opposed to a man)

Other hypernyms of selectwoman include elected official, woman.

selectwoman (noun)	adult female (noun)
a female elected member of a board of officials who run New England towns	an adult female person (as opposed to a man)