mafia
n. countablen. a large, organized group of criminals that often controls illegal businesses. It is most famous for its history in Italy and the United States.
n. a hierarchical criminal organization, typically of Italian origin, involved in racketeering and other illegal activities. When used with a lowercase 'm', it can describe any closed group that exerts secret influence in a specific field.
The police spent years investigating the local Mafia.
The documentary explores how the Mafia gained control over the city's construction industry during the mid-twentieth century.
Borrowed from Italian mafia, of uncertain origin. In the first instance, it is not clear whether the lemma in question is a Sicilian exonym or endonym, since written and oral sources on this term are scarce, the etymology remains uncertain and it's worthy of further investigation. It is possibly a regional term of the then recently established Kingdom of Italy; thus the meaning "spirit of hostility to the law" could be just derivative. The hypotheses put forward have been varied, but not very convincing from a reconstructive point of view. See Sicilian mafia for more. See, also, the Wikipedia article for more discussion of the origin of the word. Doublet of mafiya.
Capitalised when referring to the specific Italian-American or Sicilian organization; often takes a singular verb but can take a plural verb in British English.