Mediator's skill (4)
I believe the answer is:
'mediator's skill' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tact that I've seen before include "measure of diplomacy?" , "Consideration and sensitivity" , "Sensitivity in dealing with people" , "Diplomatic sensitivity" , "Delicacy of feeling, skill in saying the right thing" .)