Judge a Catholic nobleman (7)
I believe the answer is:
account
'judge' is the definition.
(I've seen this before)
'a catholic nobleman' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'nobleman' becomes 'count' (count is a kind of nobleman).
'a'+'c'+'count'='ACCOUNT'
(Other definitions for account that I've seen before include "History" , "Report of an event" , "Financial statement" , "News report" , "Tell" .)