Super ending, not beginning (7)
I believe the answer is:
topping
'super' is the definition.
(topping is old-fashioned slang for excellent)
'ending not beginning' is the wordplay.
'ending' becomes 'stopping' ('stop' can be a synonym of 'end').
'not beginning' means to remove the first letter.
'stopping' with its first letter removed is 'TOPPING'.
(Other definitions for topping that I've seen before include "Excellent; eg, icing" , "Sauce; excellent (dated)" , "murder" , "custard?" , "Garnish - splendid!" .)