grand mal has 4 distinct synonyms spread across 2 of its 2 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
epilepsy in which the attacks involve loss of consciousness and tonic spasms of the musculature followed by generalized jerking
a seizure during which the patient becomes unconscious and has convulsions over the entire body
Synonyms, antonyms and the broader and narrower relations for grand mal come from Princeton University’s WordNet. Full sources and licences.