Source : Webster's Revised Unabridged Dictionary (1913)

Jansenist \Jan"sen*ist\, n. [F. Jans['e]niste.] (Eccl. Hist.)
   A follower of Cornelius Jansen, a Roman Catholic bishop of
   Ypres, in Flanders, in the 17th century, who taught certain
   doctrines denying free will and the possibility of resisting
   divine grace.

Source : WordNet®

Jansenist
     n : an advocate of Jansenism