Bishop quietly taking on brief quarrel (7)
I believe the answer is:
pontiff
'bishop' is the definition.
(I've seen this before)
'quietly taking on brief quarrel' is the wordplay.
'quietly' becomes 'p' (musical symbol).
'taking' says to put letters next to each other.
'brief quarrel' becomes 'tiff' (I've seen this in another clue).
'p'+'on'+'tiff'='PONTIFF'
(Other definitions for pontiff that I've seen before include "Bishop" , "Title for a pope" , "Head of the Roman Catholic church" , "Religious leader" , "High-priest" .)