What is "swell mob"

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.

Swell \Swell\, a. Having the characteristics of a person of rank and importance; showy; dandified; distinguished; as, a swell person; a swell neighborhood. [Slang]

Swell mob. See under Mob. [Slang]

n. (context archaic slang English) Well-dressed thief and swindlers, regarded collectively.