Source : Webster's Revised Unabridged Dictionary (1913)

Ahriman \Ah"ri*man\, n. [Per.]
   The Evil Principle or Being of the ancient Persians; the
   Prince of Darkness as opposer to Ormuzd, the King of Light.

Source : WordNet®

Ahriman
     n : the spirit of evil in Zoroastrianism; arch rival of Ormazd