Mafia

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A secret criminal organization operating mainly in Sicily since the early 1800s and known for its intimidation of and retribution against law enforcement officials and witnesses.
• noun A secret criminal organization operating mainly in the United States and Italy and engaged in illegal activities such as gambling, drug-dealing, protection, and prostitution.
• noun Any of various similar criminal organizations, especially when dominated by members of the same nationality.
• noun Informal A tightly knit group of trusted associates, as of a political leader.

from the GNU version of the Collaborative International Dictionary of English.

• noun see maffia, maffioso.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun specifically An international criminal organization of Sicilian origin operating in Italy and the United States.
• proper noun by extension Any organized crime syndicate operating internationally in high-level organized crime; often with a modifying adjective, such as a nationality.
• proper noun Alternative capitalization of mafia (an entity which attempts to control a specified arena).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any tightly knit group of trusted associates
• noun a crime syndicate in the United States; organized in families; believed to have important relations to the Sicilian Mafia
• noun a secret terrorist group in Sicily; originally opposed tyranny but evolved into a criminal organization in the middle of the 19th century