Not able to carry a tune? That could be calumnious, nothing less (9)
I believe the answer is:
unmusical
'not able to carry a tune?' is the definition.
I can't judge whether this defines the answer.
'could be calumnious nothing less' is the wordplay.
'could be' indicates anagramming the letters.
'nothing' becomes 'O' (O resembles 0).
'less' suggests deleting specific letters (less can mean minus).
'calumnious' with 'o' taken away is 'calumnius'.
'calumnius' with letters rearranged gives 'UNMUSICAL'.
'that' is the link.
Can you help me to learn more?
(Another definition for unmusical that I've seen is " not appreciating many of these answers?".)