Transport Catholic painting (4)
I believe the answer is:
cart
'transport' is the definition.
(cart is a kind of transport)
'catholic painting' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'painting' becomes 'art' (I've seen this before**).
'c'+'art'='CART'
(Other definitions for cart that I've seen before include "Don't put this before the horse (4)" , "Open vehicle" , "Old two-wheeled goods vehicle" , "Carrying vehicle" , "Hump" .)