Zur·van·ism (zûr?v?-n?z??m)n. A Zoroastrian heretical movement claiming that Zurvan was the ultimate source of the universe and that both Ahura Mazda and Ahriman were his offspring.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.