Superlative of good (4)
I believe the answer is:
best
'superlative of good' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for best that I've seen before include "Cream of the crop" , "at 16 down [MAN UNITED] ?" , "former football star" , "Optimal" , "Supreme" .)