A conspirator is a person who takes part in a conspiracy and a conspiracy is <span>a plan done in secret by a group of people to do something unlawful or something that will cause harm to someone.</span>
An example would be:
-"Under the influence of Aurelio Saffi he became a Republican, and was arrested as a Mazzinian conspirator<span> in 1874." </span> -"His departure was accelerated by a decree of expulsion as a conspirator."