river in Hubei province
泒 is a rare kanji that names a specific river in Hubei province. Its meaning is limited to this geographic proper noun.
泒 combines the water radical 氵 with 瓜, likely as a phono-semantic compound where 瓜 suggests the sound and 氵 indicates a river name. The exact historical development is uncertain.
The water radical 氵 beside 瓜 (melon) suggests a river named after or associated with melons. Picture a river in Hubei flowing past melon fields.
For コ, imagine a child (子, こ) floating a melon (瓜) down the river (氵): こ -> コ.
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