Cunning lies - wins by design (8)
I believe the answer is:
'cunning' is the definition.
(I've seen this before)
'lies wins by design' is the wordplay.
'by' is a charade indicator (letters next to each other).
'design' indicates anagramming the letters.
'lies' after 'wins' is 'winslies'.
'winslies' with letters rearranged gives 'WILINESS'.
(Other definitions for wiliness that I've seen before include "Craft" , "Crafty, sly nature" , "Cunning" .)