belief in two equal gods, one good and one evil
• (n.) 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.
Di'the·ism noun [ Prefix di- + theism : confer French dithéisme .] 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. 
the doctrine of or belief in two equally powerful gods. · belief in the existence of two independent antagonistic principles, one good and the other evil, as in Zoroastrianism.