Room attached to a church (6)
I believe the answer is:
vestry
'room attached to a church' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for vestry that I've seen before include "Somewhere in church" , "Part of church used as an office" , "Church sacristy" , "Office room in church" , "Church robing-room" .)