Church retains property established in secret (11)
I believe the answer is:
clandestine
'secret' is the definition.
('clandestine' can be a synonym of 'secret')
'church retains property established in' is the wordplay.
'church' becomes 'ce' (abbreviation for Church of England).
'retains' means one lot of letters goes inside another.
'property' becomes 'land' (kind of property).
'established' becomes 'est' (I've seen this in other clues).
'land'+'est'+'in'='landestin'
'ce' going around 'landestin' is 'CLANDESTINE'.
(Other definitions for clandestine that I've seen before include "Surreptitious" , "Send a client (anag) - covert" , "Secret" , "Done secretly" , "Private" .)