Church area (4)
I believe the answer is:
apse
'church area' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for apse that I've seen before include "space for altar" , "Church area" , "Offshoot from the choir, nave or aisle in a church" , "Domed section of a church" , "part of cathedral" .)