Ploy sure to work (4)
I believe the answer is:
ruse
'ploy' is the definition.
(thesaurus)
'sure to work' is the wordplay.
'to work' indicates an anagram.
'sure' with letters rearranged gives 'RUSE'.
(Other definitions for ruse that I've seen before include "Deceptive tactic" , "Cunning plan" , "Ploy, artifice" , "Trick designed to deceive" , "Deceptive manoeuvre" .)