Source : Webster's Revised Unabridged Dictionary (1913)

   2. Wearing showy, counterfeit ornaments; vulgarly
      pretentious; as, flash people; flash men or women; --
      applied especially to thieves, gamblers, and prostitutes
      that dress in a showy way and wear much cheap jewelry.

   {Flash house}, a house frequented by flash people, as thieves
      and whores; hence, a brothel. ``A gang of footpads,
      reveling with their favorite beauties at a flash house.''
      --Macaulay.