crash has 18 distinct synonyms spread across 10 of its 18 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.
fall or come down violently
“The branch crashed down on my car”
move with, or as if with, a crashing noise
“The car crashed through the glass door”
move violently as through a barrier
“The terrorists crashed the gate”
occupy, usually uninvited
“My son's friends crashed our house last weekend”
make a sudden loud sound
“the waves crashed on the shore and kept us awake all night”
undergo a sudden and severe downturn
“the economy crashed”
the act of colliding with something
“his crash through the window”
(computer science) an event that causes a computer system to become inoperative
“the crash occurred during a thunderstorm and the system has been down ever since”
Synonyms, antonyms and the broader and narrower relations for crash come from Princeton University’s WordNet. Full sources and licences.