Devil's Advocate

In the old process of canonization by the Roman Catholic Church, the Devil's Advocate was a prosecutor 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 been taken to mean anyone who tests a hypothesis by taking up the opposite position to that hypothesised, even if doing so may in the long term strengthen the hypothesis.