The Collaborative International Dictionary of English v.0.48:

Subtilization \Sub`til*i*za"tion\, n. [Cf. F. subtilization.]
   1. The act of making subtile.
      [1913 Webster]

   2. (Old Chem.) The operation of making so volatile as to rise
      in steam or vapor.
      [1913 Webster]

   3. Refinement; subtlety; extreme attenuation.
      [1913 Webster]