Musicians prohibited, we're told (4)
I believe the answer is:
band
'musicians' is the definition.
(group of musicians)
'prohibited we're told' is the wordplay.
'prohibited' becomes 'banned' (synonyms).
'we're told' shows a homophone (sound like).
'banned' is a homophone of 'BAND'.
(Other definitions for band that I've seen before include "company" , "Pop group; stripe" , "Zone; group" , "Musicians - gang" , "Outline drawing" .)