Fine new missile (6)
I believe the answer is:
narrow
'fine' is the definition.
(I've seen this before)
'new missile' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'missile' becomes 'arrow' (arrow is a kind of missile).
'n'+'arrow'='NARROW'
(Other definitions for narrow that I've seen before include "Conservative" , "Close shave" , "Strait or thin" , "Constricted in width" , "Become restricted" .)