WordNet records no synonym and no antonym for league of nations. It is the only member of its synset, 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.
an international organization formed in 1920 to promote cooperation and peace among nations; although suggested by Woodrow Wilson, the United States never joined and it remained powerless; it was dissolved in 1946 after the United Nations was formed
Synonyms, antonyms and the broader and narrower relations for league of nations come from Princeton University’s WordNet. Full sources and licences.