marrow, pith, essence
髄 centers on the innermost vital substance: the marrow inside bones, the pith inside plants, or the essential core of an idea.
髄 combines 骨 (bone) with a phonetic component that historically contributed the sound ズイ and the idea of marrow or essence. The exact historical development of the right side is uncertain.
The left side 骨 means bone. The right side 迶 looks like a path leading deep inside. Picture following a path into the bone to reach the soft, vital marrow at its core.
For ズイ, imagine a tiny creature named Zui who lives inside your bones, guarding the marrow. Zui -> ズイ, and Zui's home is deep in the bone.
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spinal cord
medulla; pith
bone marrow; medulla
essence; quintessence; spirit; soul; heart; pith (and marrow)
brain; encephalon
medulla oblongata
pulp (of a tooth); dental pulp
myeloma
cervical spinal cord; cervical cord
cerebrospinal fluid hypovolemia; CSF hypovolemia; intracranial hypotension syndrome
adrenal medulla
adrenal medullary hormone
septic meningitis; purulent meningitis; suppurative meningitis
multiple myeloma
lateral medullary syndrome
enzuigiri (attack that strikes the back of the head)
enzuigiri (attack that strikes the back of the head)
marrow; pith
acute disseminated encephalomyelitis; ADEM
poliomyelitis; polio