The Collaborative International Dictionary of English v.0.48:

Syncretistic \Syn`cre*tis"tic\, a.
   1. Pertaining to, or characterized by, syncretism; as, a
      syncretistic mixture of the service of Jehovah and the
      worship of idols.
      [1913 Webster]

   2. Of or pertaining to Syncretists.
      [1913 Webster]

WordNet (r) 3.0 (2006):

syncretistic
    adj 1: relating to a historical tendency for a language to
           reduce its use of inflections; "modern English is a
           syncretic language" [syn: syncretic, syncretical,
           syncretistic, syncretistical]
    2: of or characterized by syncretism [syn: syncretic,
       syncretical, syncretistic, syncretistical]