laughter

noun

• The sound of laughing, produced by air so expelled; any similar sound.

  "Their loud laughter betrayed their presence."

• A movement (usually involuntary) of the muscles of the laughing face, particularly of the lips, and of the whole body, with a peculiar expression of the eyes, indicating merriment, satisfaction or derision, and usually attended by a sonorous and interrupted expulsion of air from the lungs.
• A reason for merriment.