white, bright, clear, pure
皜 centers on a bright, pure whiteness: something luminous, clear, and unblemished. The given meanings all flow from this idea of radiant purity.
皜 combines 白 (white) with 高 (tall, high), likely suggesting a lofty, bright whiteness. The exact historical development is uncertain, but the semantic contribution of 白 is clear.
The left side 白 is white, and the right side 高 is tall or high. Imagine a towering white pillar shining brightly under the sun, perfectly pure and clear.
For コウ, picture a bright white coat (コート) hanging high on a rack: coat -> コウ, and the coat is so white it gleams.
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