Definify.com
Webster 1913 Edition
Underwing
Un′der-wingˊ
,Noun.
1.
(Zool.)
One of the posterior wings of an insect.
2.
(Zool.)
Any one of numerous species of noctuid moths belonging to
Catocala
and allied genera, in which the hind wings are banded with red and black or other conspicuous colors. Many of the species are called red underwing
.