Calm bit of music on the radio (5)
I believe the answer is:
peace
'calm' is the definition.
(peaceful situation)
'bit of music on the radio' is the wordplay.
'bit of music' becomes 'piece' (piece of music).
'on the radio' indicates a 'sounds like' (homophone) clue.
'piece' is a homophone of 'PEACE'.
(Other definitions for peace that I've seen before include "[STILLNESS]" , "A Christmas wish" , "'Calm, harmony (5)'" , "Calm, tranquility" , "Absence of conflict" .)