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' (a vent is an opening or outlet).
'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" .)