Fine fine tune (4)
I believe the answer is:
fair
'fine' is the definition.
(I've seen this before)
'fine tune' is the wordplay.
'fine' becomes 'f' (abbreviation).
'tune' becomes 'air' (I've seen this before).
'f'+'air'='FAIR'
(Other definitions for fair that I've seen before include "Equitable - market - not bad" , "Sign following Pisces" , "The mart is blond" , "Reasonable; pretty" , "not cloudy" .)