Diplomat, with skill, shows sympathy (5)
I believe the answer is:
heart
'sympathy' is the definition.
(I've seen this in another clue)
'diplomat with skill' is the wordplay.
'diplomat' becomes 'he'.
'with' says to put letters next to each other.
'skill' becomes 'art' (both can mean a talent).
'he'+'art'='HEART'
'shows' acts as a link.
(Other definitions for heart that I've seen before include "See 22" , "Muscular organ for blood circulation" , "Core, courage" , "It's in the chest" , "Playing card - pity" .)