French film featuring old artist - tons better! (10)
I believe the answer is:
ameliorate
'better' is the definition.
(synonyms)
'french film featuring old artist tons' is the wordplay.
'french film' becomes 'amelie' (2001 French film).
'featuring' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'tons' becomes 't'.
'o'+'ra'+'t'='orat'
'amelie' going around 'orat' is 'AMELIORATE'.
(Other definitions for ameliorate that I've seen before include "seen to improve" , "Make (something) better" , "Become better" , "Make (a bad thing) better" .)