brain has 14 distinct synonyms spread across 4 of its 7 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.
that part of the central nervous system that includes all the higher nervous centers; enclosed within the skull; continuous with the spinal cord
someone who has exceptional intellectual ability and originality
“Mozart was a child genius”
the brain of certain animals used as meat
Synonyms, antonyms and the broader and narrower relations for brain come from Princeton University’s WordNet. Full sources and licences.