precipitation has 5 distinct synonyms spread across 2 of its 6 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.
the quantity of water falling to earth at a specific place within a specified period of time
“the storm brought several inches of precipitation”
the process of forming a chemical precipitate
Synonyms, antonyms and the broader and narrower relations for precipitation come from Princeton University’s WordNet. Full sources and licences.
the falling to earth of any form of water (rain or snow or hail or sleet or mist)
the act of casting down or falling headlong from a height
an unexpected acceleration or hastening
“he is responsible for the precipitation of his own demise”
overly eager speed (and possible carelessness)
“he soon regretted his haste”