Recess in a church (4)
I believe the answer is:
apse
This clue is a double definition.
'recess' is the first definition.
(apse is a kind of recess)
'church' is the second definition.
(I've seen this before)
'in a' is the link.
(Other definitions for apse that I've seen before include "Niche in church" , "Peas (anag) -- part of a church" , "Recess in church wall" , "Semicircular recess in church" , "room for an altar" .)