WordNet records no synonym and no antonym for scull. 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.
a long oar that is mounted at the stern of a boat and moved left and right to propel the boat forward
each of a pair of short oars that are used by a single oarsman
a racing shell that is propelled by sculls
Synonyms, antonyms and the broader and narrower relations for scull come from Princeton University’s WordNet. Full sources and licences.