Source : Webster's Revised Unabridged Dictionary (1913)

Subtilty \Sub"til*ty\, n. [Contr. fr. subtility.]
   1. The quality or state of being subtile; thinness; fineness;
      as, the subtility of air or light.

   2. Refinement; extreme acuteness; subtlety.

            Intelligible discourses are spoiled by too much
            subtility in nice divisions.          --Locke.

   3. Cunning; skill; craft. [Obs.]

            To learn a lewd man this subtility.   --Chaucer.

   4. Slyness in design; artifice; guile; a cunning design or
      artifice; a trick; subtlety.

            O full of all subtility and all mischief. --Acts
                                                  xiii. 10.

   Note: In senses 2, 3, and 4 the word is more commonly written
         subtlety.