1. the lower surfaces of an aircraft’s wings
Usage: aviation
2. the hindwings of insects, especially when hidden beneath the forewings
Usage: entomology

Examples

• The pilot inspected the underwings for any signs of damage before takeoff.
• Ice had formed on the aircraft’s underwings during the storm.
• The moth’s colorful underwings were revealed when it spread its wings.
• Many beetles keep their delicate underwings folded beneath protective wing covers.
• The maintenance crew checked the fuel lines running along the underwings.
• When threatened, the insect flashed its bright red underwings as a warning display.