Place where people should go on the radio (4)
I believe the answer is:
lieu
'place' is the definition.
(as in the phrase 'in lieu of')
'where people should go on the radio' is the wordplay.
'where people should go' becomes 'loo' (loo or toilet is a place to 'go').
'on the radio' shows a homophone (sound like).
'loo' is a homophone of 'LIEU'.
(Other definitions for lieu that I've seen before include "'In ..., instead (4)'" , "Stead - place" , "In - of means instead of" , "In ... of; in exchange for" , "The substitute" .)