swelling has 15 distinct synonyms spread across 3 of its 3 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.
an abnormal protuberance or localized enlargement
something that bulges out or is protuberant or projects from its surroundings
“the gun in his pocket made an obvious bulge”
the increase in volume of certain substances when they are heated (often accompanied by release of water)
Synonyms, antonyms and the broader and narrower relations for swelling come from Princeton University’s WordNet. Full sources and licences.