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.
      [1913 Webster]

            A cluster of mob were making themselves merry with
            their betters.                        --Addison.
      [1913 Webster]

   2. Hence: A throng; a rabble; esp., an unlawful or riotous
      assembly; a disorderly crowd.
      [1913 Webster]

            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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mob \Mob\, v. t. [imp. & p. p. Mobbed; p. pr. & vb. n.
   Mobbing.]
   To crowd about, as a mob, and attack or annoy; as, to mob a
   house or a person.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mob \Mob\, n. [See Mobcap.]
   A mobcap. --Goldsmith.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mob \Mob\, v. t.
   To wrap up in, or cover with, a cowl. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

mob
    n 1: a disorderly crowd of people [syn: mob, rabble, rout]
    2: a loose affiliation of gangsters in charge of organized
       criminal activities [syn: syndicate, crime syndicate,
       mob, family]
    3: an association of criminals; "police tried to break up the
       gang"; "a pack of thieves" [syn: gang, pack, ring,
       mob]
    v 1: press tightly together or cram; "The crowd packed the
         auditorium" [syn: throng, mob, pack, pile, jam]