WordNet records no synonym and no antonym for black hole of calcutta. 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.
a dungeon (20 feet square) in a fort in Calcutta where as many as 146 English prisoners were held overnight by Siraj-ud-daula; the next morning only 23 were still alive
Synonyms, antonyms and the broader and narrower relations for black hole of calcutta come from Princeton University’s WordNet. Full sources and licences.