swift has 7 distinct synonyms spread across 4 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.
United States meat-packer who began the use of refrigerated railroad cars (1839-1903)
an English satirist born in Ireland (1667-1745)
a small bird that resembles a swallow and is noted for its rapid flight
common western lizard; seen on logs or rocks
Synonyms, antonyms and the broader and narrower relations for swift come from Princeton University’s WordNet. Full sources and licences.