Father a friend of the Pope (5)
I believe the answer is:
papal
'of the pope' is the definition.
(I've seen this before)
'father a friend' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'a friend' becomes 'pal' (pal can mean a friend).
'pa'+'pal'='PAPAL'
(Other definitions for papal that I've seen before include "of Catholic high-up" , "Relating to the Pontiff" , "Like some bulls" , "Of the highest Vatican authority" , "Of the RC leader" .)