King, for one, blocking distasteful pope (7)
I believe the answer is:
gregory
'pope' is the definition.
(I know that Gregory is an pope)
'king for one blocking distasteful' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'for one' becomes 'eg' (both can mean 'for example').
'blocking' means one lot of letters goes inside another.
'distasteful' becomes 'gory' (as in 'gory details').
'r'+'eg'='reg'
'reg' put within 'gory' is 'GREGORY'.
(Other definitions for gregory that I've seen before include "boy" , "Calendar-reforming pope" , "Boy's name meaning "watcher"" , "pope, perhaps" .)