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 subsidiary indication.
'star' becomes 'idol' (idol is a kind of star).
'on the radio' indicates a 'sounds like' (homophone) clue.
'idol' is a homophone of 'idle'.
(Other definitions for idle that I've seen before include "Out of work", "Not active or at work", "'Lazy, not doing anything (4)'", "Not hardworking", "Do very little", "Not being used", "Monty Python's Eric, b. 1943", "Not busy", "Workshy" and "Not working".)