smash has 21 distinct synonyms spread across 11 of its 16 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.
hit violently
“She smashed her car against the guard rail”
hit (a tennis ball) in a powerful overhead stroke
collide or strike violently and suddenly
“The motorcycle smashed into the guard rail”
overthrow or destroy (something considered evil or harmful)
“The police smashed the drug ring after they were tipped off”
break suddenly into pieces, as from a violent blow
“The window smashed”
the act of colliding with something
“his crash through the window”
Synonyms, antonyms and the broader and narrower relations for smash come from Princeton University’s WordNet. Full sources and licences.