Illuminated large object (3)
I believe the answer is:
lit
'illuminated' is the definition.
(synonyms)
'large object' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'object' becomes 'it' (pronoun for an inanimate object).
'l'+'it'='LIT'
(Other definitions for lit that I've seen before include "books etc?" , "Fired" , "Set afire" , "Creative writing, in short" , "Set fire to" .)