Saint in charge with a large church (8)
I believe the answer is:
basilica
'large church' is the definition.
(type of large church or cathedral)
'saint in charge with a' is the wordplay.
'saint' becomes 'basil' (I've seen this before).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'with' is a charade indicator (letters next to each other).
'basil'+'ic'+'a'='BASILICA'
(Other definitions for basilica that I've seen before include "A large Christian church with two rows of columns (8)" , "Magnificent church" , "Church or cathedral of high rank" , "Roman Catholic cathedral with special privileges" , "Large Christian church with two rows of columns and apse at one end" .)