The Collaborative International Dictionary of English v.0.48:
Mob \Mob\, n. [L. mobile vulgus, the movable common people. See
1. The lower classes of a community; the populace, or the
lowest part of it.
A cluster of mob were making themselves merry with
their betters. --Addison.
2. Hence: A throng; a rabble; esp., an unlawful or riotous
assembly; a disorderly crowd.
The mob of gentlemen who wrote with ease. --Pope.
Had every Athenian citizen been a Socrates, every
Athenian assembly would still have been a mob.
Confused by brainless mobs. --Tennyson.
3. A criminal organization or organized criminal gangs,
collectively; the Mafia; the syndicate; as, he was a
lawyer for the mob.
Mob law, law administered by the mob; lynch law.
Swell mob, well dressed thieves and swindlers, regarded
collectively. [Slang] --Dickens.