laughter

Etymology

From Middle English laughter, laghter, laȝter, from Old English hleahtor (“laughter, jubilation, derision”), from Proto-Germanic *hlahtraz (“laughter”), from Proto-Indo-European *klek-, *kleg- (“to shout”). Cognate with German Gelächter (“laughter, hilarity, merriment”), Danish and Norwegian latter (“laughter”), Icelandic hlátur (“laughter”). More at laugh.

noun

1. The sound of laughing, produced by air so expelled; any similar sound.
   Their loud laughter betrayed their presence.
   There was some laughter, and Roddle was left free to expand his ideas on the periodic visits of cowboys to the town. 1899, Stephen Crane, chapter 1, in Twelve O'Clock
2. 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.
3. (archaic) A reason for merriment.