Furtive, sly (6)
I believe the answer is:
sneaky
I believe this is a double definition.
'furtive' is the first definition.
(I know that furtive can be written as sneaky)
'sly' is the second definition.
(I've seen this in another clue)
(Other definitions for sneaky that I've seen before include "Cunning" , "Sly and devious" , "Furtive or given to telling tales" , "Being furtive or underhanded" , "Deceitful, underhand" .)