(neuroanatomy) grey matter

brain / head / chief, principal

central part or heart, especially of a city

(neuroanatomy) white matter

quality

the color white / (by extension) innocence / (go) a white go stone / something unwritten / (colloquial) the white team in a 紅白 (kōhaku) group / (colloquial) an unlicensed prostitute

center, middle, heart, core (physical center) / center, hub (most important area of activity) / crux, main point

(anatomy) the brain / (by extension, figuratively) one's brains, one's mental functioning

(archaic, anatomy) the brain / (archaic, by extension) the head

ash; ashes