red mole, cinnabar
硃 centers on a red mineral substance: cinnabar, the bright red ore, and by extension a red mole or mark on the skin that resembles its color.
硃 combines 石 (stone) with 朱 (vermillion, red), indicating a red mineral or stone. The character likely originated as a specific term for cinnabar ore.
A red stone 石 marked with vermillion 朱: this is cinnabar, the mineral that gives a bright red color, like a red mole on the skin.
For シュ, imagine a shoe made of red cinnabar stone: shoe -> シュ, and the red stone 硃 is as bright as the shoe.
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