Cunningly clever (6)
I believe the answer is:
artful
'cunningly clever' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for artful that I've seen before include "Crafty or cunning" , "Cunning, wily" , "Oliver Twist's pal was an . . . . . . dodger" , "Crafty like Dicken's Dodger" , "Unnatural - cunning" .)