Английский Этимологический словарь - slang

- 1756, "special vocabulary of tramps or thieves," later "jargon of a particular profession" (1801), of uncertain origin, perhaps from a Scandinavian source, cf. Norw. slengenavn "nickname," related to O.N. slyngva "to sling." Sense of "very informal language characterized by vividness and novelty" first recorded 1818. A word that ought to have survived is slangwhanger (1807, Amer.Eng.) "noisy or abusive talker or writer."