Musicians not allowed to be heard (4)
I believe the answer is:
band
'musicians' is the definition.
(group of musicians)
'not allowed to be heard' is the wordplay.
'not allowed' becomes 'banned'.
'to be heard' shows a homophone (sound like).
'banned' sounds like 'BAND'.
(Other definitions for band that I've seen before include "Musicians - circle" , "troop" , "Pop group; stripe" , "Music ensemble" , "Players" .)