This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
渻 combines 氵 (water) with 省, but the historical development and original meaning are uncertain.
The water radical 氵 beside 省 suggests something related to water, but the specific meaning is not established. Think of it as a mysterious water-related character.
For セイ, imagine a calm lake where you say 'say' to the water: say -> セイ, and the water listens quietly.
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