1570s, "religious puritan" (implied in Catharism), from Medieval Latin Cathari "the Pure," name taken by Novatians and other Christian sects, from New Testament Greek katharizein "to make clean," from Greek katharos "pure" (see catharsis). Especially in reference to the 12c. sects (Albigenses, etc.) in Languedoc and the Piedmont that denied the authority of Rome. Related: Catharist.