Excellent, marvellous (6)
I believe the answer is:
superb
This clue is a double definition.
'excellent' is the first definition.
(I've seen this before)
'marvellous' is the second definition.
(I've seen this before)
(Other definitions for superb that I've seen before include "'Excellent, brilliant (6)'" , "Of surpassing excellence" , "Excellent, magnificent" , "First-rate" , "choice" .)