This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
濹 is a rare character combining 氵 (water) with 墨 (ink). It likely refers to ink-black water or a river name, but the exact historical development is uncertain.
Water 氵 beside ink 墨 suggests a river dark as ink. Imagine a stream flowing with the color of black ink.
For ボク, picture a bottle of black ink (墨) floating on the water: the ink's reading ボク cues the same sound for 濹.
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