Very large Mail cartoons reproduced (12)
I believe the answer is:
astronomical
'very large' is the definition.
(I've seen this before)
'mail cartoons reproduced' is the wordplay.
'reproduced' is an anagram indicator (I've seen 'reproduce' mean this).
'mail'+'cartoons'='mailcartoons'
'mailcartoons' anagrammed gives 'ASTRONOMICAL'.
(Other definitions for astronomical that I've seen before include "Extremely large" , "Absolutely huge, in a heavenly way" , "Inconceivably large" , "Of the study of stars" , "Really, really big" .)