river in Henan province
溮 is a rare kanji that refers specifically to a river in Henan province. Its meaning is a proper name rather than a general concept.
溮 combines the water radical 氵 with the phonetic component 師, suggesting a name for a body of water. The exact historical development is uncertain.
The water radical 氵 beside 師 points to a specific river. Imagine a teacher (師) standing by the water, naming it after the river in Henan.
For シ, picture the river she (シ) flows through Henan: she -> シ, and the water radical 氵 marks it as a river.
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