The Collaborative International Dictionary of English v.0.48:

Mithraicism \Mithraicism\ prop. n.
   Mithraism.

   Syn: .
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Mithraicism
    n 1: ancient Persian religion; popular among Romans during first
         three centuries a.d. [syn: Mithraism, Mithraicism]