Quietly tell high-ranking member of the clergy (7)
I believe the answer is:
prelate
'high-ranking member of the clergy' is the definition.
(prelate is a type of bishop)
'quietly tell' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'tell' becomes 'relate' (as in to tell or relate a story).
'p'+'relate'='PRELATE'
(Other definitions for prelate that I've seen before include "Senior churchman" , "e.g. Bishop" , "Church high-ranker" , "priest" , "Senior member of the clergy" .)