Lazy star on the radio (4)
I believe the answer is:
Here is my best explanation:
'lazy' is the definition.
('idle' can be similar in meaning to 'lazy')
'star on the radio' is the wordplay.
'star' becomes 'idol' (idol is a kind of star).
'on the radio' shows a homophone (sound like).
'idol' sounds like 'IDLE'.
(Other definitions for idle that I've seen before include "Explosive stuff", "At rest", "Unoccupied or not in use", "not working in > lounge", "having been taken from service", "Out of work", "not being engaged", "Do very little", "Run out of gear" and "Circus entertainer".)