invasion of iwo has 2 distinct synonyms spread across 1 of its 1 sense. 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.
a bloody and prolonged operation on the island of Iwo Jima in which American marines landed and defeated Japanese defenders (February and March 1945)
Synonyms, antonyms and the broader and narrower relations for invasion of iwo come from Princeton University’s WordNet. Full sources and licences.