Catholic getting on in prison (5)
I believe the answer is:
caged
'in prison' is the definition.
(caged can mean imprisoned)
'catholic getting on' is the wordplay.
'catholic' becomes 'C' (abbreviation as in RC for Roman Catholic).
'getting on' becomes 'aged' (getting on can mean getting older).
'c'+'aged'='CAGED'
(Other definitions for caged that I've seen before include "Shut up" , "in prison" , "Confined behind bars" , "Cooped up" , "In a zoo?" .)