Covetousness secures nothing for diplomat (5)
I believe the answer is:
envoy
'diplomat' is the definition.
(envoy is a kind of diplomat)
'covetousness secures nothing' is the wordplay.
'covetousness' becomes 'envy' (I've seen this before).
'secures' is an insertion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'envy' enclosing 'o' is 'ENVOY'.
'for' acts as a link.
(Other definitions for envoy that I've seen before include "Plenipotentiary" , "Diplomatic representative" , "One sent on a mission" , "Diplomatic messenger" , "Diplomat" .)