Devil's advocate
In the old process of canonization by the Roman Catholic Church, the Devil's Advocate was a canon lawyer appointed by the Church to argue against the canonization of the proposed candidate. In Latin, the title, which is unofficial, is advocatvs diaboli, which would perhaps be more accurately translated into English by the phrase the Devil's lawyer. The official title is Fidei Defensor, Latin for Defender of the Faith.
Since then, the term has come to mean anyone who argues a position that he does not believe in, simply for the sake of arguing; or to present a counterargument for a position he does believe in to another debater, for the purpose of testing the quality of the counterargument and identifying weaknesses in his own argument.
The Devil's Advocate was also a 1997 film starring Keanu Reeves and Al Pacino.
