Underwing

/ˌʌndˈɜːwəɹɪŋ/

/ˌʌndˈɜːwəɪŋ/

Underwing

the feathers on the underside of a bird's wing, which can have distinctive patterns and colors that are often visible in flight

moth having dull forewings and brightly colored hind wings

Examples

1. Okay, well if this underwing area is dark, then the underwing area of the wing in the back will be dark as well.