Dictionary:

conspirator

  (kən-spîr'ə-tər)

One that engages in a conspiracy.

noun

One who assists a lawbreaker in a wrongful or criminal act: accessory, accomplice, confederate. See crimes, help/harm/harmless.

One involved in a conspiracy; one who acts with another, or others, in furtherance of an unlawful transaction. "It is not necessary that all of the conspirators either meet together or agree simultaneously. . . . It is not necessary that each member of a conspiracy know the exact part which every other participant is playing; nor is it necessary in order to be bound by the acts of his associates that each member of a conspiracy shall know all the other participants therein; nor is it requisite that simultaneous action be had for those who come on later, and cooperate in the common effort to obtain the unlawful results, to become parties thereto and assume responsibility for all that has been done before." 47 F. Supp. 395, 400-01. According to the Model Penal Code, a conspirator is one who, with another person or persons with the purpose of promoting or facilitating the commission of a crime "a) agrees with such other person or persons that they or one or more of them will engage in conduct which constitutes such crime or an attempt or solicitation to commit such crime; or b) agrees to aid such other person or persons in the planning or commission of such crime or an attempt or solicitation to commit such crime." Model Penal Code §5.03(1).

The noun has one meaning:

Meaning #1: a member of a conspiracy
  Synonyms: coconspirator, plotter, machinator