Church area, not left to pass into disuse (4)
I believe the answer is:
apse
'church area' is the definition.
(I've seen this before)
'not left to pass into disuse' is the wordplay.
'not' suggests deleting specific letters.
'left' becomes 'l' (common abbreviation).
'to pass into disuse' becomes 'lapse' (I've seen this before).
'lapse' with 'l' taken out is 'APSE'.
(Other definitions for apse that I've seen before include "Part of a church with the altar" , "Rounded end of building" , "Primate holds saint to be a" , "Church recess in lapsed condition" , "Where the altar is usually found in a church" .)