The Collaborative International Dictionary of English v.0.48:

Theosophist \The*os"o*phist\, n.
   One addicted to theosophy.
   [1913 Webster]

         The theosophist is one who gives you a theory of God,
         or of the works of God, which has not reason, but an
         inspiration of his own, for its basis.   --R. A.
                                                  Vaughan.
   [1913 Webster]

WordNet (r) 3.0 (2006):

theosophist
    n 1: a believer in theosophy