Revolutionary trend ? Roman Catholic belief (6)
I believe the answer is:
credit
'belief' is the definition.
(thesaurus)
'revolutionary trend ? roman catholic' is the wordplay.
'revolutionary' is a reversal indicator.
'trend ?' becomes 'tide' (I've seen this before).
'roman catholic' becomes 'rc' ('r.c.' can be a synonym of 'roman catholic').
'tide'+'rc'='tiderc'
'tiderc' reversed gives 'CREDIT'.
(Other definitions for credit that I've seen before include "Praise; tick" , "Belief; tick" , "gives you a good result in examination" , "Have faith" , "If this is good, you can borrow money" .)