Source : Webster's Revised Unabridged Dictionary (1913)

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.

            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.
                                                  --Madison.

            Confused by brainless mobs.           --Tennyson.

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

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