With meaningless opening word, joined broadcast (5)
I believe the answer is:
sowed
'broadcast' is the definition.
(broadcast can mean to sow seeds)
'with meaningless opening word joined' is the wordplay.
'with meaningless opening word' becomes 'so' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'joined' becomes 'we'd' (I've seen this in another clue).
'so'+'wed'='SOWED'
Can you help me to learn more?
(Other definitions for sowed that I've seen before include "Scattered seed" , "Placed seeds in the ground" , "broadcast" .)