broadcast has 16 distinct synonyms spread across 3 of its 5 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
broadcast over the airwaves, as in radio or television
“We cannot air this X-rated song”
sow over a wide area, especially by hand
“broadcast seeds”
cause to become widely known
“spread information”
message that is transmitted by radio or television
a radio or television show
“did you see his program last night?”
Synonyms, antonyms and the broader and narrower relations for broadcast come from Princeton University’s WordNet. Full sources and licences.