The Collaborative International Dictionary of English v.0.48:

Catharist \Cath"a*rist\, n. [LL. catharista, fr. Gr. ? clean,
   pure.]
   One aiming at or pretending to a greater purity of like than
   others about him; -- applied to persons of various sects. See
   Albigenses.
   [1913 Webster]