Leader in priesthood, say (7)
I believe the answer is:
prelate
'leader' is the definition.
(prelate is a kind of leader)
'priesthood say' is the wordplay.
'priesthood' becomes 'p' (this could be a standard abbreviation I've not previously seen).
'say' becomes 'relate' (as in relating a story).
'p'+'relate'='PRELATE'
'in' is the link.
(Other definitions for prelate that I've seen before include "Bishop perhaps" , "Senior churchman" , "Cleric" , "High-ranking clergyman" , "priest" .)