Make better, improve (10)
I believe the answer is:
ameliorate
This clue is a double definition.
'make better' is the first definition.
(synonyms)
'improve' is the second definition.
(synonyms)
(Other definitions for ameliorate that I've seen before include "Make (something) better" , "Make (a bad thing) better" , "Become better" , "seen to improve" .)