Demand work on radio (4)
I believe the answer is:
need
'demand' is the definition.
('need' can be a synonym of 'demand')
'work on radio' is the wordplay.
'work' becomes 'knead' ('knead' can be a synonym of 'work').
'on radio' indicates a 'sounds like' (homophone) clue.
'knead' is a homophone of 'NEED'.
(Other definitions for need that I've seen before include "Rely on" , "privation" , "must have results!" , "Necessity" , "Distressful situation" .)