Definitions of flap:

• noun:   any broad thin and limber covering attached at one edge; hangs loose or projects freely

  Example: "He wrote on the flap of the envelope"

• noun:   a movable airfoil that is part of an aircraft wing; used to increase lift or drag
• noun:   a movable piece of tissue partly connected to the body
• noun:   the motion made by flapping up and down
• noun:   an excited state of agitation

  Example: "There was a terrible flap about the theft"

• verb:   pronounce with a flap, of alveolar sounds
• verb:   move noisily

  Example: "Flags flapped in the strong wind"

• verb:   move with a flapping motion

  Example: "The bird's wings were flapping"

• verb:   move with a thrashing motion

  Example: "The bird flapped its wings"

• verb:   make a fuss; be agitated
• verb:   move in a wavy pattern or with a rising and falling motion