c. 1300, "pack of animals" (a sense now obsolete), of uncertain origin, but possibly related to Middle English rablen "to gabble, speak in a rapid, confused manner" (mid-14c.), which is probably imitative of hurry, noise, and confusion (compare Middle Dutch rabbelen, Low German rabbeln "to chatter").
The meaning "tumultuous crowd of vulgar, noisy people" is from late 14c., probably a back-formation from the Middle English verb. It was applied contemptuously to the common or low part of any populace, regardless of tumult, by 1550s.
"iron bar, bent at right angles at one end, for stirring molten metal," 1864, from French râble, from Old French roable, from Latin rutabulum "rake, fire shovel" (in Medieval Latin also rotabulum), from ruere "to churn or plow up, dig out," (from PIE *reuo-, source also of Sanskrit ravisam, ravat "to wound, hurt;" Lithuanian ráuti "to tear out, pull," ravėti "to weed;" Russian ryt'i, roju "to dig," Old Church Slavonic rylo "spade," Old Norse ryja "to tear out wool," German roden "to root out").
"the rabble, the lowest order of people collectively," 1670s, from French canaille (16c.), from Italian canaglia, literally "a pack of dogs," from cane "dog," from Latin canis (from PIE root *kwon- "dog").
mid-14c., rascaile "people of the lowest class, the general mass; rabble or foot-soldiers of an army" (senses now obsolete), also singular, "low, tricky, dishonest person," from Old French rascaille "rabble, mob" (12c., Modern French racaille), as Cotgrave's French-English Dictionary (1611) defines it: "the rascality or base and rascall sort, the scumme, dregs, offals, outcasts, of any company."
This is of uncertain origin, perhaps a diminutive from Old French rascler, from Vulgar Latin *rasicare "to scrape" (see rash (n.)) on the notion of "the scrapings." "[U]sed in objurgation with much latitude, and often, like rogue, with slight meaning" [Century Dictionary]. Used also in Middle English of animals unfit to chase as game on account of some quality, especially a lean deer. Also formerly an adjective.
1680s, "disorderly part of the population, rabble, common mass, the multitude, especially when rude or disorderly; a riotous assemblage," slang shortening of mobile, mobility "common people, populace, rabble" (1670s, probably with a conscious play on nobility), from Latin mobile vulgus "fickle common people" (the Latin phrase is attested c. 1600 in English), from mobile, neuter of mobilis "fickle, movable, mobile" (see mobile (adj.)).
Mob is a very strong word for a tumultuous or even riotous assembly, moved to or toward lawlessness by discontent or some similar exciting cause. Rabble is a contemptuous word for the very lowest classes, considered as confused or without sufficient strength or unity of feeling to make them especially dangerous. [Century Dictionary, 1897]
Also used of a promiscuous aggregation of people in any rank of life (1680s), and in Australia and New Zealand used without disparagement for "a crowd." Meaning "gang of criminals working together" is from 1839, originally of thieves or pick-pockets; the American English sense of "organized crime in general" is from 1927.
The Mob was not a synonym for the Mafia. It was an alliance of Jews, Italians, and a few Irishmen, some of them brilliant, who organized the supply, and often the production, of liquor during the thirteen years, ten months, and nineteen days of Prohibition. ... Their alliance — sometimes called the Combination but never the Mafia — was part of the urgent process of Americanizing crime. [Pete Hamill, "Why Sinatra Matters," 1998]
Mob scene "crowded place" is by 1922, from earlier use in reference to movies and theatrical productions; mob-rule "ochlocracy" is by 1806.
early 15c. in astronomy, "outer sphere of the universe" (the primum mobile), from mobile (adj.); the artistic sense "abstract sculpture consisting of parts suspended so as to move," associated with Alexander Calder, is by 1939, perhaps a shortening of mobile sculpture (1936). Now-obsolete sense of "the common people, the rabble" (1670s, short for Latin mobile vulgus) led to mob (n.). Middle English had moble, moeble (mid-14c.) "movable goods, personal property," from Old French moble, meuble, from the Latin adjective, but in 16c. this was replaced by furniture.
1897, from German Lumpenproletariat, coined by Marx, who used it in the sense of "the rabble, poorest of the working class," "who make no contribution to the workers' cause" [OED]. From German lump "ragamuffin," which is related to lumpen "a rag, tatter," probably ultimately related to English lump (n.). With proletariat.
Marx used it first, apparently, in 1850 in German newspaper articles collected and republished in 1895 as "Die Klassenkämpfe in Frankreich 1848-1850." Its secondary sense of "boorish, stupid people" led to lumpen- being taken as a word-forming element meaning "unenlightened."