Collapsed round part of holy place (4)
I believe the answer is:
apse
'holy place' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'collapsed round part' is the wordplay.
'part' says the answer is hidden in the clue.
'APSE' can be found hidden inside 'collapsed round'.
'of' is the link.
Can you help me to learn more?
(Other definitions for apse that I've seen before include "Church's part" , "Domed section of a church" , "Rounded end of building" , "Peas (anag) -- part of a church" , "Architectural feature in a church" .)