Sacristy (6)
I believe the answer is:
vestry
'sacristy' is the definition.
(synonyms)
This is all the clue.
(Other definitions for vestry that I've seen before include "Somewhere in church" , "Church sacristy" , "Parochial meeting-room in church" , "Storage and dressing room in a church" , "Small room attached to church" .)