noun (n)

• a secret agreement between two or more people to perform an unlawful act(noun.communication)

  Synonym:
  confederacy
  

  source: wordnet30
• a plot to carry out some harmful or illegal act (especially a political plot)(noun.cognition)

  Synonym:
  cabal
  

  source: wordnet30
• a group of conspirators banded together to achieve some harmful or illegal purpose(noun.group)

  source: wordnet30
• A combination of men for an evil purpose; an agreement, between two or more persons, to commit a crime in concert, as treason; a plot.(noun)

  source: webster1913