The Collaborative International Dictionary of English v.0.48:

Wily \Wil"y\, a. [Compar. Wilier; superl. Wiliest.] [From
   Wile.]
   Full of wiles, tricks, or stratagems; using craft or
   stratagem to accomplish a purpose; mischievously artful;
   subtle. "Wily and wise." --Chaucer. "The wily snake."
   --Milton.
   [1913 Webster]

         This false, wily, doubling disposition of mind.
                                                  --South.
   [1913 Webster]

   Syn: Cunning; artful; sly; crafty. See Cunning.
        [1913 Webster]