The Collaborative International Dictionary of English v.0.48:

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

   Mob law, law administered by the mob; lynch law.

   Swell mob, well dressed thieves and swindlers, regarded
      collectively. [Slang] --Dickens.
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