Diplomat's asset (4)
I believe the answer is:
tact
'diplomat's asset' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tact that I've seen before include "Delicacy of feeling, skill in saying the right thing" , "Sensitivity (in dealing with others)" , "Consideration and sensitivity" , "Skill in dealing with people" , "Understanding" .)