A really good note to end on. Great (6)
I believe the answer is:
superb
'great' is the definition.
(thesaurus)
'a really good note' is the wordplay.
'a really good' becomes 'super' (I am not sure about this - if you are sure you should believe this answer much more).
'note' becomes 'b' (musical note).
'super'+'b'='SUPERB'
'to end on' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for superb that I've seen before include "Surpassingly good" , "Dusty product of spider" , "choice" , "Wonderful, really great" , "Highly impressive" .)