Couple failing to start broadcast (3)
I believe the answer is:
air
'broadcast' is the definition.
(to air on TV)
'couple failing to start' is the wordplay.
'couple' becomes 'pair' (synonyms).
'failing to start' means to remove the first letter.
'pair' with its first letter taken off is 'AIR'.
(Other definitions for air that I've seen before include "Feel" , "Publish" , "Display" , "Ventilate or give expression to" , "Sky" .)