Slang, n.
Etymology: [Said to be of Gypsy origin; but probably from Scand., and akin to E. sling; cf. Norw. sleng a slinging, an invention, device, slengja to sling, to cast, slengja kjeften (literally, to sling the jaw) to use abusive language, to use slang, slenjeord (ord = word) an insulting word, a new word that has no just reason for being.]
Low, vulgar, unauthorized language; a popular but unauthorized word, phrase, or mode of expression; also, the jargon of some particular calling or class in society; low popular cant; as, the slang of the theater, of college, of sailors, etc.
4 other Webster entries under this spelling
Slang
imp. of Sling. Slung. [Archaic]
Slang, n.
Any long, narrow piece of land; a promontory. [Local, Eng.] Holland.
Slang, n.
A fetter worn on the leg by a convict. [Eng.]
Slang, v. t. [imp. & p. p. Slanged; p. pr. & vb. n. Slanging.]
To address with slang or ribaldry; to insult with vulgar language. [Colloq.] Every gentleman abused by a cabman or slanged by a bargee was bound there and then to take off his coat and challenge him to fisticuffs. London Spectator.
Shades of meaning
A colloquialism is an expression not coarse or low, and perhaps not incorrect, but below the literary grade; educated persons are apt to allow themselves some colloquialisms in familiar conversation, which they would avoid in writing or public speaking. Slang, in the primary sense, denotes expressions that are either coarse and rude in themselves or chiefly current among the coarser and ruder part of the community; there are also many expressions current in special senses in certain communities that may be characterized as slang; as, college slang; club slang; racing slang. In the evolution of language many words originally slang are adopted by good writers and speakers, and ultimately take their place as accepted English. A vulgarism is an expression decidedly incorrect, and the use of which is a mark of ignorance or low breeding. Cant, as used in this connection, denotes the barbarous jargon used as a secret language by thieves, tramps, etc. Compare diction; language.