Marvellous month ending with a starry event (9)
I believe the answer is:
supernova
'starry event' is the definition.
(explosion of a star)
'marvellous month ending with a' is the wordplay.
'marvellous' becomes 'super' (I've seen this before).
'month' becomes 'nov' (abbreviation for November).
'ending with' means one lot of letters go next to another.
'super'+'nov'+'a'='SUPERNOVA'
(Other definitions for supernova that I've seen before include "cosmic explosion" , "Star in decline" , "Star made brilliant by stellar explosion" , "Exploding star that becomes much brighter" , "it puts an end to a starry career" .)