Excellent, never-ending melody (3)
I believe the answer is:
air
'melody' is the definition.
(I know that melody can be written as air)
'excellent never-ending' is the wordplay.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'ending' suggests the final letters (the ending of the word).
The final letter of 'never' is 'r'.
'ai'+'r'='AIR'
(Other definitions for air that I've seen before include "Ventilate, say grievance" , "Demeanour" , "Simple tune" , "Simple composition" , "Cool" .)