A large painting outside (8)
I believe the answer is:
alfresco
'outside' is the definition.
(I've seen this before)
'a large painting' is the wordplay.
'large' becomes 'l'.
'painting' becomes 'fresco' (fresco is a kind of painting**).
'a'+'l'+'fresco'='ALFRESCO'
(Other definitions for alfresco that I've seen before include "Out of doors" , "where it's cool" , "Meal eaten in the outdoors" , "out of the house" , "In the open air" .)