Laughter v. i. : A movement (usually involuntary) of the muscles of the face, particularly of the lips, 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. See Laugh, v. i.

Example:
Laughter...............................?

Taxonomy
laughter, laugh, humor, the brain, human laughter, Contagious Laughter, Health, cause laughter, theory, mechanism, Laughter Yoga, New York, Nervous laughter, free encyclopedia, Research, inconsistency, humans, danger.

Defination from the web:
Laughter is used as a signal for being part of a group — it signals acceptance and positive interactions with others. ... Recently researchers have shown infants as early as 17 days old have vocal laughing sounds or laughter. ...