Right to employ a ploy (4)
I believe the answer is:
ruse
'a ploy' is the definition.
(I've seen this in other clues)
'right to employ' is the wordplay.
'right' becomes 'r' (abbreviation).
'to employ' becomes 'use' ('use' can be a synonym of 'employ').
'r'+'use'='RUSE'
(Other definitions for ruse that I've seen before include "Plan intended to deceive" , "Deceptive tactic" , "trick played" , "Sue to be a ploy" , "Trick designed to deceive" .)