The Collaborative International Dictionary of English v.0.48:

Maffia \Maf"fi*a\, Mafia \Ma"fi*a\, n. [It. maffia.]
   1. A secret society which organized in Sicily as a political
      organization, but is now widespread among Italians, and is
      used to further or protect private interests, reputedly by
      illegal methods; called also the Sicilian Mafia.
      [WordNet sense 2]
      [Webster 1913 Suppl.]

   2. A group of loosely associated of criminal organizations in
      the United States, some having ties to the Sicilian Mafia,
      and organized in "families"; the term is applied to the
      entire group of organizations, or to any one local group.
      Also, loosely, organized groups of criminals anywhere, as
      the Russian mafia. [WordNet sense 1]

   Syn: syndicate, mob, Cosa Nostra, La Cosa Nostra, organized
        crime.
        [WordNet 1.6 + PJC]

   3. Any tightly knit group of trusted associates having strong
      control or influence in some area; as, Kennedy and his
      Irish Mafia. [informal] [WordNet sense 3]
      [PJC]

WordNet (r) 3.0 (2006):

Sicilian Mafia
    n 1: a secret terrorist group in Sicily; originally opposed
         tyranny but evolved into a criminal organization in the
         middle of the 19th century [syn: Mafia, Maffia,
         Sicilian Mafia]