The Collaborative International Dictionary of English v.0.48:

Hypostatize \Hy*pos"ta*tize\, v. t.
   1. To make into, or regarded as, a separate and distinct
      substance.
      [1913 Webster]

            Looked upon both species and genera as hypostatized
            universals.                           --Pop. Sci.
                                                  Monthly.
      [1913 Webster]

   2. To attribute actual or personal existence to. --Sir W.
      Hamilton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hypostatize
    v 1: construe as a real existence, of a conceptual entity [syn:
         hypostatize, hypostatise]