The Collaborative International Dictionary of English v.0.48:

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.
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   2. To refine; to spin into niceties; as, to subtilize
      arguments.
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            Nor as yet have we subtilized ourselves into
            savages.                              --Burke.
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