腦

Phono-semantic compound, composed of:

Semantic element: 肉 (“flesh”), indicating a body organ.

Phonetic / conceptual element: 巛 (“winding stream”) + 囟 (“fontanelle / crown of the head”) — together forming the ancient root character.

Historically, the portion 巛 + 囟 was itself an older independent character pronounced "no", representing the structure of the head. Later writing systems added 肉 to clarify the anatomical meaning.

A common traditional interpretation explains the structure as follows:

The fontanelle (囟) + the winding, flowing form of nerves (巛) + the flesh (肉), together depict the brain, the soft, convoluted organ inside the skull.

《說文解字》 (Shuowen Jiezi):

「腦，首膚也。从肉，𦣝聲。」

“腦 means the soft flesh of the head. Formed from 肉 with 𦣝 as the phonetic.”

(𦣝 is the ancient form of 囟 + 巛)

뇌수 (腦水) — brain material, brain matter

뇌신경 (腦神經) — cranial nerve

뇌졸중 (腦卒中) — stroke

두뇌 (頭腦) — intellect

전뇌 (前腦) — forebrain

중뇌 (中腦) — midbrain

후뇌 (後腦) — hindbrain

좌뇌 (左腦) — left hemisphere

우뇌 (右腦) — right hemisphere

뇌압 (腦壓) — intracranial pressure

뇌염 (腦炎) — encephalitis

뇌하수체 (腦下垂體) — pituitary gland

Traditional East Asian medicine treated the brain as the “Sea of Marrow” (髓海).

Classical citations:

《淮南子 · 精神訓》 (Huainanzi)

「腦者，髓之海也。」

“The brain is the sea of the marrow.”

(An important early physiological description.)

《靈樞經 · 海論》 (part of the Huangdi Neijing, classical medical text)

「腦為髓海。」

“The brain is the ‘Sea of Marrow.’”

(Highly influential in East Asian medicine.)

《史記 · 扁鵲倉公列傳》 (Records of the Grand Historian)

「腦滿耳熱。」

“The brain swells and the ears grow hot.”

(Description of symptoms in ancient medical diagnosis.)