Where does the term Devil's Advocate come from?

It originated in the Catholic Church. When someone is recommended for Sainthood, the church appoints 'advocatus Dei' as the promoter of the cause to represent the evidence to support the granting of sainthood. They also appoint a the 'advocatus diaboli' or Devil's Advocate to argue against the canonization. This is to insure that they have looked at all angles of the canonization from a theological standpoint.