English definition of “flap”
/flæp/ verb (present participle flapping, past tense and past participle flapped)
WINGS [T] › If a bird flaps its wings, it moves them up and down.
MOVE [I] › If something such as cloth or paper flaps, the side that is not fixed to something moves around, especially in the wind: The curtains were flapping around in the breeze.
WORRY [I] UK informal › to become worried or excited about something: Don't flap! We've got plenty of time to get to the airport.