The Collaborative International Dictionary of English v.0.48:

Mystagogue \Mys"ta*gogue\, n. [L. mystagogus, Gr. ?; ? one
   initiated in mysteries + ? leading, n., a leader, fr. ? to
   lead: cf. F. mystagogue. See 1st Mystery.]
   1. One who interprets mysteries, especially of a religious
      kind.
      [1913 Webster]

   2. One who keeps and shows church relics.
      [1913 Webster]