Collapsed around church part (4)
I believe the answer is:
apse
'church part' is the definition.
('apse' is part of 'church')
'collapsed around' is the wordplay.
'around' indicates the answer is hidden within the clue.
'APSE' is hidden within 'collapsed'.
(Other definitions for apse that I've seen before include "Church area" , "Recess at east end of church" , "inside church?" , "In sacred space" , "room for an altar" .)