cushion has 4 distinct synonyms spread across 2 of its 4 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.
a mechanical damper; absorbs energy of sudden impulses
“the old car needed a new set of shocks”
the layer of air that supports a hovercraft or similar vehicle
Synonyms, antonyms and the broader and narrower relations for cushion come from Princeton University’s WordNet. Full sources and licences.
a soft bag filled with air or a mass of padding such as feathers or foam rubber etc.