WordNet records no synonym and no antonym for ganymede. It is the only member of each of its synsets, 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.
(Greek mythology) a Trojan boy who was so beautiful that Zeus carried him away to serve as cupbearer to the gods
the largest of Jupiter's satellites
Synonyms, antonyms and the broader and narrower relations for ganymede come from Princeton University’s WordNet. Full sources and licences.