wall of silence has 2 distinct synonyms spread across 1 of its 1 sense. 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.
the secrecy of police officers who lie or look the other way to protect other police officers
“the blue wall cracked when some officers refused to take part in the cover-up”
Synonyms, antonyms and the broader and narrower relations for wall of silence come from Princeton University’s WordNet. Full sources and licences.