pass away has 14 distinct synonyms spread across 1 of its 2 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.
pass from physical life and lose all bodily attributes and functions necessary to sustain life
“She died from cancer”
go out of existence
“She hoped that the problem would eventually pass away”
Synonyms, antonyms and the broader and narrower relations for pass away come from Princeton University’s WordNet. Full sources and licences.