WordNet records no synonym and no antonym for shad. 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.
bony flesh of herring-like fish usually caught during their migration to fresh water for spawning; especially of Atlantic coast
herring-like food fishes that migrate from the sea to fresh water to spawn
Synonyms, antonyms and the broader and narrower relations for shad come from Princeton University’s WordNet. Full sources and licences.