Most excellent (4)
'most excellent' is the definition.
(the very best)
This is all the clue.
(Other definitions for best that I've seen before include "Most excellent; outwit" , "at 16 down [MAN UNITED] ?" , "Limit of one's ability" , "12 21[FOOTBALLER" , "To the highest standard" .)
'most excellent' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for supreme that I've seen before include "Highest in authority; rich cream sauce (dish)" , "Paramount" , "Creamy sauce" , "Chief" , "Greatest in status, authority or power" .)
(Other definitions for greatest that I've seen before include "Best-ever" , "Largest or most distinguished" , "Not to be surpassed" , "Most important!" , "Get stare from the mightiest" .)