Word Origin & History
slang1756, "special vocabulary of tramps or thieves," later "jargon of a particular profession" (1801), of uncertain origin, perhaps from a Scandinavian source, cf. Norw. slengenamn "nickname," slengja kjeften "to abuse with words," lit. "to sling the jaw," related to O.N. slyngva "to sling." But OED, while
admitting "some approximation in sense," discounts this connection based on "date and early associations." 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."