vast
澒 centers on vastness, especially of water, suggesting an immense, boundless expanse.
澒 combines 氵 (water) with 項, which likely contributes the sound. The exact historical development is uncertain.
The water radical 氵 beside 項 (item) suggests an item so vast it's like an ocean: 澒 is vastness.
For コウ, imagine a vast ocean cove: cove -> コウ, and the water stretches endlessly.
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