Clever, sharp (6)
I believe the answer is:
shrewd
I believe this is a double definition.
'clever' is the first definition.
(I've seen this in another clue)
'sharp' is the second definition.
(I know that sharp can be written as shrewd)
(Other definitions for shrewd that I've seen before include "Craftily astute" , "... knowing" , "worldly wise" , "Having good judgment" , "Clever and calculating" .)