Sure to use stratagem (4)
I believe the answer is:
ruse
'stratagem' is the definition.
(a ruse is a stratagem or ploy)
'sure to use' is the wordplay.
'to use' is an anagram indicator (I've seen 'used' mean this).
'sure' anagrammed gives 'RUSE'.
(Other definitions for ruse that I've seen before include "Cunning scheme" , "Clever stratagem or plan" , "Trick designed to deceive" , "Deceptive manoeuvre" , "Cunning plan" .)