laughter

n. act of laughing; sound which expresses amusement (or scorn, etc.); cheerfulness, mirthfulness

Laughter is an audible expression or appearance of merriment or amusement or an inward feeling of joy and pleasure(laughing on the inside). It may ensue (as a physiological reaction) from jokes, tickling and other stimuli. Inhaling nitrous oxide can also induce laughter; other drugs, such as cannabis, can also induce episodes of strong laughter. Strong laughter can sometimes bring an onset of tears or even moderate muscular pain as a physical response to the act. Laughter can also be a response to physical touch, such as tickling, or even to moderate pain such as pressure on the ulnar nerve ("funny bone").
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Noun
1. the sound of laughing
(synonym) laugh
(hypernym) utterance, vocalization
(hyponym) cachinnation
2. the activity of laughing; the manifestation of joy or mirth of scorn; "he enjoyed the laughter of the crowd"
(hypernym) activity

(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.