commonwealth has 8 distinct synonyms spread across 2 of its 4 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 official name of some states in the United States (Massachusetts and Pennsylvania and Virginia and Kentucky) and associated territories (Puerto Rico)
a politically organized body of people under a single government
“the state has elected a new president”
a world organization of autonomous states that are united in allegiance to a central power but are not subordinate to it or to one another
a political system in which the supreme power lies in a body of citizens who can elect people to represent them
Synonyms, antonyms and the broader and narrower relations for commonwealth come from Princeton University’s WordNet. Full sources and licences.