advocatus diaboli
/advəʊˈkeɪtəs daɪˈabəlaɪ/ /advəˈkɑːtəs diˈabəli/noun
= devil's advocate.
Origin
Early 19th century; earliest use found in Henry Crabb Robinson (1775–1867), diarist and journalist. From post-classical Latin advocatus diaboli from classical Latin advocātus + diabolī, genitive of diabolus.