so has 10 distinct synonyms spread across 5 of its 11 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.
in truth (often tends to intensify)
“they said the car would break down and indeed it did”
the syllable naming the fifth (dominant) note of any musical scale in solmization
6 of the 11 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for so.
Synonyms, antonyms and the broader and narrower relations for so come from Princeton University’s WordNet. Full sources and licences.