Prisoner opening religious community (7)
I believe the answer is:
convent
'religious community' is the definition.
(I've seen this before)
'prisoner opening' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'opening' becomes 'vent' (vent is a kind of opening).
'con'+'vent'='CONVENT'
(Other definitions for convent that I've seen before include "Community of nuns" , "Religious community" , "Nunnery" , "place for nuns" , "Building for prayer" .)