Shrewd, perceptive (6)
I believe the answer is:
astute
This clue is a double definition.
'shrewd' is the first definition.
(I know that shrewd can be written as astute)
'perceptive' is the second definition.
(I've seen this before)
(Other definitions for astute that I've seen before include "Able to assess (people or situations) accurately" , "Discerning" , "intelligent" , "Shrewd, quick to spot advantage" , "Canny and sagacious" .)