Church changing room (6)
I believe the answer is:
vestry
'church changing room' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for vestry that I've seen before include "Church sacristy" , "Church room where clergy dress themselves" , "Part of church used as an office" , "Small room attached to church" , "Storage and dressing room in a church" .)