Source : Webster's Revised Unabridged Dictionary (1913)

Subtile \Sub"tile\, a. [L. subtilis. See {Subtile}.]
   1. Thin; not dense or gross; rare; as, subtile air; subtile
      vapor; a subtile medium.

   2. Delicately constituted or constructed; nice; fine;
      delicate; tenuous; finely woven. ``A sotil [subtile]
      twine's thread.'' --Chaucer.

            More subtile web Arachne can not spin. --Spenser.

            I do distinguish plain Each subtile line of her
            immortal face.                        --Sir J.
                                                  Davies.

   3. Acute; piercing; searching.

            The slow disease and subtile pain.    --Prior.

   5. Characterized by nicety of discrimination; discerning;
      delicate; refined; subtle. [In this sense now commonly
      written {subtle}.]

            The genius of the Spanish people is exquisitely
            subtile, without being at all acute; hence there is
            so much humor and so little wit in their literature.
            The genius of the Italians, on the contrary, is
            acute, profound, and sensual, but not subtile; hence
            what they think to be humorous, is merely witty.
                                                  --Coleridge.

            The subtile influence of an intellect like
            Emerson's.                            --Hawthorne.

   5. Sly; artful; cunning; crafty; subtle; as, a subtile
      person; a subtile adversary; a subtile scheme. [In this
      sense now commonly written {subtle}.]

   Syn: {Subtile}, {Acute}.

   Usage: In acute the image is that of a needle's point; in
          subtile that of a thread spun out to fineness. The
          acute intellect pierces to its aim; the subtile (or
          subtle) intellect winds its way through obstacles. --
          {Sub"tile*ly}, adv. -- {Sub"tile*ness}, n.