Church nook (4)
I believe the answer is:
apse
'church nook' 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 "Where you could find a magistrate's chair" , "Church recess in lapsed condition" , "Peas (anag) -- part of a church" , "Peas (anag) - found in church" , "Domed section of a church" .)