brown has 9 distinct synonyms spread across 7 of its 8 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.
an orange of low brightness and saturation
Scottish botanist who first observed the movement of small particles in fluids now known a Brownian motion (1773-1858)
abolitionist who was hanged after leading an unsuccessful raid at Harper's Ferry, Virginia (1800-1859)
fry in a pan until it changes color
“brown the meat in the pan”
of a color similar to that of wood or earth
(of skin) deeply suntanned
Synonyms, antonyms and the broader and narrower relations for brown come from Princeton University’s WordNet. Full sources and licences.