\Sub"tle\, a. [Compar. {Subtler}; superl. {Subtlest}.]
[OE. sotil, subtil, OF. soutil, later subtil, F. subtil, L.
subtilis; probably, originally, woven fine, and fr. sub under
+ tela a web, fr. texere to weave. See {Text}, and cf.
{Subtile}.]
1. Sly in design; artful; cunning; insinuating; subtile; --
   applied to persons; as, a subtle foe. ``A subtle
   traitor.'' --Shak.
2. Cunningly devised; crafty; treacherous; as, a subtle
   stratagem.
3. Characterized by refinement and niceness in drawing
   distinctions; nicely discriminating; -- said of persons;
   as, a subtle logician; refined; tenuous; sinuous;
   insinuating; hence, penetrative or pervasive; -- said of
   the mind; its faculties, or its operations; as, a subtle
   intellect; a subtle imagination; a subtle process of
   thought; also, difficult of apprehension; elusive.
         Things remote from use, obscure and subtle.
                                               --Milton.
4. Smooth and deceptive. [Obs.]
         Like to a bowl upon a subtle ground [bowling
         ground].                              --Shak.
Syn: Artful; crafty; cunning; shrewd; sly; wily.
Usage: Subtle is the most comprehensive of these epithets and
       implies the finest intellectual quality. See {Shrewd},
       and {Cunning}.