Thus united by the broadcast? (5)
I believe the answer is:
sowed
'the broadcast?' is the definition.
(broadcast can mean to sow seeds)
'thus united by' is the wordplay.
'thus' becomes 'so' (synonyms).
'united' becomes 'we'd' (united in marriage).
'by' is a charade indicator (letters next to each other).
'so'+'wed'='SOWED'
(Other definitions for sowed that I've seen before include "broadcast" , "Scattered seed" , "Placed seeds in the ground" .)