vast, expansive, deep, dirty
濊 centers on vastness and depth, especially of water, but also carries a sense of murkiness or dirtiness. The meanings range from expansive and deep to dirty, suggesting a large body of water that is not clear.
濊 combines 氵 (water) with 歲, which likely contributes the sound. The exact historical development is uncertain, but the water radical suggests a connection to large or deep bodies of water.
Water 氵 combined with the complex 歲 suggests a vast, deep expanse of water that has become murky and dirty over time.
For カイ, imagine a vast, deep sea that looks like a dark, dirty 'kai' (sea) — the word 'kai' itself cues カイ, and the scene matches the kanji's meaning of vast, deep, dirty water.
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