underwing vs owlet moth

underwing and owlet moth both are nouns.

Word	Noun	Adjective	Verb	Adverb
underwing	Yes	No	No	No
owlet moth	Yes	No	No	No

As nouns, owlet moth is a hypernym of underwing; that is, owlet moth is a word with a broader meaning than underwing:

underwing: moth having dull forewings and brightly colored hind wings
owlet moth: usually dull-colored medium-sized nocturnal moth; the usually smooth-bodied larvae are destructive agricultural pests

Other hypernyms of underwing include noctuid, noctuid moth.

underwing (noun)	owlet moth (noun)
moth having dull forewings and brightly colored hind wings	usually dull-colored medium-sized nocturnal moth; the usually smooth-bodied larvae are destructive agricultural pests