federation has 2 distinct synonyms spread across 1 of its 3 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.
an organization formed by merging several groups or parties
the act of constituting a political unity out of a number of separate states or colonies or provinces so that each member retains the management of its internal affairs
Synonyms, antonyms and the broader and narrower relations for federation come from Princeton University’s WordNet. Full sources and licences.