bosom has 9 distinct synonyms spread across 4 of its 8 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.
the chest considered as the place where secret thoughts are kept
“his bosom was bursting with the secret”
cloth that covers the chest or breasts
hide in one's bosom
“She bosomed his letters”
Synonyms, antonyms and the broader and narrower relations for bosom come from Princeton University’s WordNet. Full sources and licences.