ˌnʌlɪfɪˈkeɪʃən əʊ.vəˈɹaɪd oʊ.vəɹˈɹaɪd the act of nullifying; making null and void; counteracting or overriding the effect or force of something the states'-rights doctrine that a state can refuse to recognize or to enforce a federal law passed by the United States Congress