respire has 3 distinct synonyms spread across 1 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.
breathe easily again, as after exertion or anxiety
undergo the biomedical and metabolic processes of respiration by taking up oxygen and producing carbon monoxide
draw air into, and expel out of, the lungs
“I can breathe better when the air is clean”
Synonyms, antonyms and the broader and narrower relations for respire come from Princeton University’s WordNet. Full sources and licences.