Smile for broadcast (4)
I believe the answer is:
beam
I believe this is a double definition.
'smile' is the first definition.
(to beam is to smile)
'broadcast' is the second definition.
(synonyms)
'for' acts as a link.
(Other definitions for beam that I've seen before include "Ray; piece of timber" , "Gymnast's bar; broad smile" , "Ray - large piece of wood" , "Light - heavy timber - wide smile" , "A broad smile like lunar ray" .)