WordNet records no synonym and no antonym for states' rights. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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 doctrine that federal powers should be curtailed and returned to the individual states
the rights conceded to the states by the United States constitution
Synonyms, antonyms and the broader and narrower relations for states' rights come from Princeton University’s WordNet. Full sources and licences.