WordNet records no synonym and no antonym for scylla. 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.
(Greek mythology) a sea nymph transformed into a sea monster who lived on one side of a narrow strait; drowned and devoured sailors who tried to escape Charybdis (a whirlpool) on the other side of the strait
Synonyms, antonyms and the broader and narrower relations for scylla come from Princeton University’s WordNet. Full sources and licences.