keep quiet 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. Its one recorded opposite is talk.
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.
refrain from divulging sensitive information; keep quiet about confidential information
“Don't tell him any secrets--he cannot keep his mouth shut!”
Synonyms, antonyms and the broader and narrower relations for keep quiet come from Princeton University’s WordNet. Full sources and licences.