The Collaborative International Dictionary of English v.0.48:

Magna Mater \Magna Mater\ prop. n.
   A great nature goddess of ancient Phrygia in Asia Minor; the
   counterpart of the Greek Rhea and the Roman Ops.

   Syn: Cybele, Dindymene, Great Mother, Mater Turrita.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Magna Mater
    n 1: great nature goddess of ancient Phrygia in Asia Minor;
         counterpart of Greek Rhea and Roman Ops [syn: Cybele,
         Dindymene, Great Mother, Magna Mater, Mater
         Turrita]