laughter

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act of laughing.
2. n. The sound produced by laughing.
3. n. Archaic A cause or subject for laughter.

Century Dictionary and Cyclopedia

1. n. A mode of expressing mirth, consisting chiefly in certain convulsive and partly involuntary actions of the muscles of respiration, by means of which, after an inspiration, the expulsion of the air from the chest in a series of jerks produces a succession of short abrupt sounds, accompanied by certain movements of the muscles of the face, and often of other parts of the body, and, when excessive, by tears: also sometimes applied to any expression of merriment perceivable in the countenance. Laughter, accompanied by a feeling of annoyance rather than merriment, may be caused by tickling; it also accompanies hysteria.
2. n. A laugh.

Wiktionary

1. n. The sound of laughing, produced by air so expelled; any similar sound.
2. n. A movement (usually involuntary) of the muscles of the laughing 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.
3. n. A reason for merriment

GNU Webster's 1913

1. n. 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.

WordNet 3.0

1. n. the sound of laughing
2. n. the activity of laughing; the manifestation of joy or mirth or scorn