cracker has 5 distinct synonyms spread across 3 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. 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.
a thin crisp wafer made of flour and water with or without leavening and shortening; unsweetened or semisweet
a programmer who cracks (gains unauthorized access to) computers, typically to do malicious things
“crackers are often mistakenly called hackers”
firework consisting of a small explosive charge and fuse in a heavy paper casing
a party favor consisting of a paper roll (usually containing candy or a small favor) that pops when pulled at both ends
Synonyms, antonyms and the broader and narrower relations for cracker come from Princeton University’s WordNet. Full sources and licences.