miˈthrēəm noun
( plural mith·raea -ēə ; also mithraeums )
Usage: usually capitalized
Etymology: New Latin, from Greek Mithraion shrine of Mithras, from Mithras, Persian god of light and defender of truth, from Old Persian Mithra — more at miter
: an underground room simulating a cave used for mithraic rites (as initiations)