Stratagem, ruse (4)
I believe the answer is:
ploy
This clue is a double definition.
'stratagem' is the first definition.
(I know that stratagem can be written as ploy)
'ruse' is the second definition.
(both can mean a trick or scheme)
(Other definitions for ploy that I've seen before include "'Stratagem, gambit (4)'" , "Trick" , "Device" , "Cunning manoeuvre to gain advantage" , "Clever tactic" .)