1the hindwing of an insect, especially when it is normally hidden by a forewing.
2the underside of a bird’s wing.
3 (also underwing moth) [usually with modifier] a moth with drab forewings and brightly coloured hindwings, typically yellow with a black terminal band.
Several genera in the family Noctuidae.
underwing in other Oxford dictionaries
Definition of underwing in the US English dictionary
