Church niche (4)
I believe the answer is:
apse
'church niche' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for apse that I've seen before include "In sacred space" , "Recess at eastern end of a church" , "Church recess with domed or arched roof" , "Primate holds saint to be a" , "Where you could find a magistrate's chair" .)