This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
洚 combines 氵 (water) with 夅, which likely contributes the sound. The exact historical development is uncertain.
Water 氵 beside 夅, but the meaning is unclear. Think of it as a mysterious water-related character.
For コウ, imagine a koi fish swimming in the water 氵 beside 夅: koi -> コウ.
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