A friend keeping varied role around island is better (10)
I believe the answer is:
ameliorate
'is better' is the definition.
(to ameliorate is to make better)
'a friend keeping varied role around island' is the wordplay.
'friend' becomes 'mate' (mate is a kind of friend).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'varied' indicates an anagram.
'around' indicates putting letters inside.
'island' becomes 'i' (geographical abbreviation).
'role' with letters rearranged gives 'elor'.
'elor' going around 'i' is 'elior'.
'mate' placed around 'elior' is 'meliorate'.
'a'+'meliorate'='AMELIORATE'
(Other definitions for ameliorate that I've seen before include "Make (a bad thing) better" , "Become better" , "Make (something) better" , "seen to improve" .)