Source : Webster's Revised Unabridged Dictionary (1913)

Subtilize \Sub"til*ize\, v. t. [imp. & p. p. {Subtilized}; p.
   pr. & vb. n. {Subtilizing}.] [L. subtiliser.]
   1. To make thin or fine; to make less gross or coarse.

   2. To refine; to spin into niceties; as, to subtilize
      arguments.

            Nor as yet have we subtilized ourselves into
            savages.                              --Burke.

Subtilize \Sub"til*ize\, v. i.
   To refine in argument; to make very nice distinctions.
   --Milner.

Source : WordNet®

subtilize
     v 1: mark fine distinctions and subtleties, as among words
     2: make more subtle or refined [syn: {rarefy}, {sublimate}]
     3: make (senses) more keen [syn: {subtilise}]