A sect of Christians, who held the doctrines of Cornelius Jansen, Bishop of Ypres, in France. Jansen professed to have formulated the teaching of Augustine, A.D. 1640, which resembled Calvinism in many respects. He taught the doctrines of “irresistible grace,” “original sin,” and the “utter helplessness of the natural man to turn to God.” Louis XIV. took part against them, and they were put down by Pope Clement XI., in 1705, in the famous bull called Unigenitus (q.v.).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Jansenists from Fact Monster: