underwing

/ˈʌndərˌwɪŋ/
noun
  1. The lower surface of a bird's wing, especially when it has a different color or pattern from the upper surface.
    • The bird's underwing feathers are often hidden when it is perched.
    • The hawk's underwing was pale with dark streaks.
    • We could see the bright white underwing of the gull as it flew overhead.
  2. A type of moth (family Noctuidae) that has brightly colored hindwings, often hidden when the moth is at rest.
    • The underwing's hidden orange bands are a defense against predators.
    • An underwing moth landed on the porch light last night.
    • Children love to find underwing moths resting on tree trunks during the day.
  3. A person or thing that provides support or protection, like a figurative wing.
    • She found an underwing in her teacher, who encouraged her to write.
    • The mentor acted as an underwing for the young artist's career.
    • The charity served as an underwing for families in need.