Group is prohibited, we hear (4)
I believe the answer is:
band
'group' is the definition.
(band can mean a group of people)
'prohibited we hear' is the wordplay.
'prohibited' becomes 'banned' (banning is a kind of prohibiting).
'we hear' shows a homophone (sound like).
'banned' sounds like 'BAND'.
'is' is the link.
(Other definitions for band that I've seen before include "Musicians - circle" , "Zone; group" , "troop" , "Pop group, perhaps" , "company" .)