older uses refer to schools in Ireland begun 1733 by the Charter Society to provide Protestant education to poor Catholic children. Modern use in U.S. began c. 1988, as an alternative to state-run public education.
"one who advocates the contrary side," 1760, translating Latin advocatus diaboli, in the Catholic Church, a promoter of the faith and officer of the Sacred Congregation of Rites whose job it is to urge against the canonization of a candidate for sainthood. "[F]ar from being the whitewasher of the wicked, the [devil's advocate] is the blackener of the good." [Fowler]. Said to have been first employed in connection with the beatification of St. Lorenzo Giustiniani under Leo X (1513-21).
mid-15c. (late 13c. in Anglo-French), "royal writ to determine by what warrant a person holds an office or franchise," a Medieval Latin legal phrase, literally "by what warrant," from quo "from, with, or by whom or what?," ablative of the interrogative pronoun quis "who?" (from PIE root *kwo-, stem of relative and interrogative pronouns). Also see warrant (n.).