Primate embraces son in church recess (4)
I believe the answer is:
apse
'church recess' is the definition.
(I've seen this before)
'primate embraces son' is the wordplay.
'primate' becomes 'ape' (I've seen this before).
'embraces' is an insertion indicator.
'son' becomes 's'.
'ape' enclosing 's' is 'APSE'.
'in' acts as a link.
(Other definitions for apse that I've seen before include "Strange peas in the church recess" , "Projection to the east end of a church" , "Rounded end of building" , "In sacred space" , "Peas (anag) -- part of a church" .)