Cunning, deceitful (3)
I believe the answer is:
sly
This clue is a double definition.
'cunning' is the first definition.
(I know that cunning can be written as sly)
'deceitful' is the second definition.
(I've seen this in another clue)
(Other definitions for sly that I've seen before include "Crafty, devious" , "'Cunning, wily (3)'" , "Doing things in unpleasant and secret way" , "Cunning, deceitful" , "Artful" .)