Thanks court for diplomacy (4)
I believe the answer is:
tact
'diplomacy' is the definition.
(thesaurus)
'thanks court' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'court' becomes 'ct'.
'ta'+'ct'='TACT'
'for' acts as a link.
(Other definitions for tact that I've seen before include "measure of diplomacy?" , "Sensitivity in dealing with people" , "Diplomatic skill" , "Sensitivity in dealings" , "Skill in dealing with people" .)