precipitate has 6 distinct synonyms spread across 2 of its 7 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.
bring about abruptly
“The crisis precipitated by Russia's revolution”
separate as a fine suspension of solid particles
fall vertically, sharply, or headlong
“Our economy precipitated into complete ruin”
hurl or throw violently
“The bridge broke and precipitated the train into the river below”
done with very great haste and without due deliberation
“hasty marriage seldom proveth well”
Synonyms, antonyms and the broader and narrower relations for precipitate come from Princeton University’s WordNet. Full sources and licences.