WordNet records no synonym and no antonym for rosetta stone. 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 part of an inscribed granite stela that was originally about six feet tall and was set up in 196 BC; the inscriptions in hieroglyphics and Demotic and Greek gave the first clues to the decipherment of Egyptian hieroglyphics
Synonyms, antonyms and the broader and narrower relations for rosetta stone come from Princeton University’s WordNet. Full sources and licences.