volatile has 2 distinct synonyms spread across 2 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. Its one recorded opposite is nonvolatile.
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.
evaporating readily at normal temperatures and pressures
“volatile oils”
a volatile substance; a substance that changes readily from solid or liquid to a vapor
“it was heated to evaporate the volatiles”
1 of the 5 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for volatile.
Synonyms, antonyms and the broader and narrower relations for volatile come from Princeton University’s WordNet. Full sources and licences.