Union's denial broadcast (4)
I believe the answer is:
knot
'union's' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'denial broadcast' is the wordplay.
'denial' becomes 'not'.
'broadcast' indicates a 'sounds like' (homophone) clue (how the word might sound on the radio or TV).
'not' is a homophone of 'KNOT'.
Can you help me to learn more?
(Other definitions for knot that I've seen before include "Fastening; sea bird" , "To secure < > bird" , "Eg, hitch" , "Tie; a cluster" , "securing tie" .)