1911 Encyclopædia Britannica/Laughter

LAUGHTER, the visible and audible expression of mirth, pleasure or the sense of the ridiculous by movements of the facial muscles and inarticulate sounds (see Comedy, Play and Humour). The O. Eng. hleahtor is formed from hleahhan, to laugh, a common Teutonic word; cf. Ger. lachen, Goth. hlahjan, Icel. hlaeja, &c. These are in origin echoic or imitative words, to be referred to a Teut. base hlah-, Indo-Eur. kark-, to make a noise; Skeat (Etym. Dict., 1898) connects ultimately Gr. κλώσσειν, to cluck like a hen, κράζειν, to croak, &c. A gentle and inaudible form of laughter expressed by a movement of the lips and by the eyes is a “smile.” This is a comparatively late word in English, and is due to Scandinavian influence; cf. Swed. smila; it is ultimately connected with Lat. mirari, to wonder, and probably with Gr. μεῖδος.