Our musical arrangement is marvellous (10)
I believe the answer is:
miraculous
'marvellous' is the definition.
(I know that marvellous can be written as miraculous)
'our musical arrangement' is the wordplay.
'arrangement' indicates anagramming the letters.
'our'+'musical'='ourmusical'
'ourmusical' anagrammed gives 'MIRACULOUS'.
'is' is the link.
(Other definitions for miraculous that I've seen before include "Incredibly wonderful" , "supernatural achievement" , "amazing" .)