This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
硣 combines 石 (stone) with 孝, but the exact historical development and original meaning are uncertain.
The stone radical 石 suggests something related to rock or mineral, but without a known meaning, it is best remembered as a stone paired with the 孝 component.
For コウ, imagine a stone monument dedicated to filial piety (孝, こう): the stone 石 and 孝 together cue コウ.
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