the great calamity has 3 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 famine in Ireland resulting from a potato blight; between 1846 and 1851 a million people starved to death and 1.6 million emigrated (most to America)
Synonyms, antonyms and the broader and narrower relations for the great calamity come from Princeton University’s WordNet. Full sources and licences.