Catholic left to admit fool (5)
I believe the answer is:
clown
'fool' is the definition.
(I know that clown is a type of fool)
'catholic left to admit' is the wordplay.
'catholic' becomes 'C' (abbreviation as in RC for Roman Catholic).
'left' becomes 'l' (common abbreviation).
'to admit' becomes 'own' (own can mean to admit or acknowledge).
'c'+'l'+'own'='CLOWN'
(Other definitions for clown that I've seen before include "Jester" , "Harlequin" , "Zany performer" , "Slapstick entertainer" , "Act comically" .)