nullification has 1 distinct synonym spread across 1 of its 2 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 states'-rights doctrine that a state can refuse to recognize or to enforce a federal law passed by the United States Congress
the act of nullifying; making null and void; counteracting or overriding the effect or force of something
Synonyms, antonyms and the broader and narrower relations for nullification come from Princeton University’s WordNet. Full sources and licences.