The Collaborative International Dictionary of English v.0.48:

Ditheism \Di"the*ism\, n. [Pref. di- + theism: cf. F.
   dith['e]isme.]
   The doctrine of those who maintain the existence of two gods
   or of two original principles (as in Manicheism), one good
   and one evil; dualism.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "ditheism":
   acosmism, allotheism, anthropolatry, anthropomorphism,
   anthropotheism, autotheism, cosmotheism, deism, dualism, dyotheism,
   henotheism, hylotheism, monolatry, monotheism, multitheism,
   myriotheism, pantheism, physicomorphism, physitheism, polytheism,
   psychotheism, tetratheism, theism, theopantism, theriotheism,
   tritheism, zootheism