Diplomacy in charge of subterfuge (6)
I believe the answer is:
tactic
'subterfuge' is the definition.
(thesaurus)
'diplomacy in charge' is the wordplay.
'diplomacy' becomes 'tact' (tact can mean diplomacy or sensitivity).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'tact'+'ic'='TACTIC'
'of' is the link.
(Other definitions for tactic that I've seen before include "Ruse, strategy" , "Military manoeuvre" , "Planned manoeuvre or skilful move" , "Ploy, strategem" , "A skilful manoeuvre or procedure" .)