Broadcast end of 'open sesame' as a group (2,5)
I believe the answer is:
'as a group' is the definition.
('en masse' can be a synonym of 'as a group')
'broadcast end of open sesame' is the wordplay.
'broadcast' indicates anagramming the letters.
'end of' suggests the final letters.
The last letter of 'open' is 'n'.
'nsesame' with letters rearranged gives 'EN MASSE'.
(Other definitions for en masse that I've seen before include "Sees man (anag.)" , "Many as one" , "All together as a group" , "All together - in France (2.5)" , "All together (Fr.)" .)