intransitive verb
Definition: To move quickly and lightly, often by beating the air with wings or arms, or to become upset or flustered.
Example: The bird began to flap its wings as it prepared to take off.
noun
Definition: A flat piece that is attached on one side and can move or cover something, like the part of an envelope that closes it or a part of an aircraft wing that helps it fly.
Example: She opened the envelope and carefully lifted the flap to read the letter inside.
transitive verb
Definition: To move something quickly up and down or from side to side, often making a fluttering sound.
Example: She decided to flap the flag to get everyone's attention.