Source : Webster's Revised Unabridged Dictionary (1913)

Zoroastrianism \Zo`ro*as"tri*an*ism\, n.
   The religious system of Zoroaster, the legislator and prophet
   of the ancient Persians, which was the national faith of
   Persia; mazdeism. The system presupposes a good spirit
   (Ormuzd) and an opposing evil spirit (Ahriman). Cf. {Fire
   worship}, under {Fire}, and {Parsee}.

Source : WordNet®

Zoroastrianism
     n : system of religion founded in Persia in the 6th century BC
         by Zoroaster; set forth in the Zend-Avesta; based on
         concept of struggle between light (good) and dark (evil)
         [syn: {Mazdaism}]