Some devout Catholics backed diplomacy (4)
I believe the answer is:
tact
'diplomacy' is the definition.
(tact can mean diplomacy or sensitivity)
'some devout catholics backed' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'backed' shows that the letters should be reversed in order.
'tcat' is hidden within 'devout catholics'.
'tcat' backwards is 'TACT'.
(Other definitions for tact that I've seen before include "Consideration and sensitivity" , "Diplomatic skill" , "Diplomacy or discretion" , "Skill in dealing with people" , "Diplomatic sensitivity" .)