Zoroastrianism

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The religious system founded by Zoroaster and set forth in the Avesta, teaching the worship of Ahura Mazda in the context of a universal struggle between the forces of light and of darkness.

from The Century Dictionary.

• noun The system of religious doctrine taught by Zoroaster and his followers in the Avesta; the religion prevalent in Persia till its overthrow by the Mohammedans in the seventh century, and still held by the Guebers and Parsees, and commonly, though incorrectly, called fire-worship.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• proper noun General usage: Religion and philosophy based on the teachings ascribed to the prophet Zoroaster.
• proper noun Scholastic usage: identifies the religion as it exists today, as distinguished from earlier forms of the religion. (see Related terms, below).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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)