Domed or vaulted recess at the east end of a church (4)
I believe the answer is:
apse
(Other definitions for apse that I've seen before include "Peas (anag) - found in church" , "Semicircular end of a church, behind the altar" , "may be seen in church!" , "Projection to the east end of a church" , "where praetor sat" .)