Vulgar programme on radio (6)
I believe the answer is:
coarse
'vulgar' is the definition.
(I know that vulgar can be written as coarse)
'programme on radio' is the wordplay.
'programme' becomes 'course' (programme of study).
'on radio' shows a homophone (sound like).
'course' sounds like 'COARSE'.
(Other definitions for coarse that I've seen before include "Rude, vulgar" , "Rough in texture or crude in manner" , "Rough or crude, lacking refinement" , "Large-grained or rough to the touch" , "Inferior" .)