This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
硄 combines 石 (stone) with 光 (light), but its historical origin and original meaning are uncertain. It may have been a character for a type of stone or a variant of another character.
A stone 石 that shines with light 光, but its actual meaning is unknown.
For コウ, imagine a glowing stone that makes a deep 'koh' sound when struck: koh -> コウ.
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