The Collaborative International Dictionary of English v.0.48:

Manichaean \Man`i*chae"an\, Manichean \Man`i*che"an\, Manichee
\Man"i*chee\, n. [LL. Manichaeus: cf. F. manich['e]en.]
   A believer in the doctrines of Manes, a Persian of the third
   century A. D., who taught a dualism in which Light is
   regarded as the source of Good, and Darkness as the source of
   Evil.
   [1913 Webster]

         The Manichaeans stand as representatives of dualism
         pushed to its utmost development.        --Tylor.
   [1913 Webster] Manichaean

The Collaborative International Dictionary of English v.0.48:

Manichaean \Man`i*chae"an\, Manichean \Man`i*che"an\, a.
   Of or pertaining to the Manichaeans.
   [1913 Webster] Manichaeism

WordNet (r) 3.0 (2006):

Manichaean
    adj 1: of or relating to the philosophical doctrine of dualism;
           "a Manichaean conflict between good and evil" [syn:
           dualistic, Manichaean]
    2: of or relating to Manichaeism [syn: Manichaean,
       Manichean, Manichee]
    n 1: an adherent of Manichaeism [syn: Manichaean, Manichean,
         Manichee]