Fine tune objective (4)
I believe the answer is:
fair
'objective' is the definition.
(thesaurus)
'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 "Average" , "Trade exhibition, (of weather) fine" , "Blonde; impartial" , "Satisfactory" , "The mart is blond" .)