name of Chinese river
渭 is a proper noun referring to a specific Chinese river, the Wei River. It has no general conceptual meaning beyond this geographic name.
渭 combines 氵 (water) with 胃, which likely contributes the sound. It was created as a specific river name.
The water radical 氵 beside 胃 suggests a river whose name sounds like 胃. Picture a river flowing past a stomach-shaped bend.
For イ, imagine the Wei River as an 'e' shaped waterway: the letter 'e' sounds like イ and marks the river's name.
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