hollow, pit, depression, swamp
洼 centers on a low-lying, water-filled depression in the ground: a hollow, pit, or swampy area.
洼 combines 氵 (water) with 圭, which likely contributes the sound. The character expresses a water-filled hollow or depression.
Water 氵 collects in a low spot shaped like the stacked earth 圭, forming a muddy pit or swamp.
For アイ, imagine an eye-shaped hollow filled with water: eye -> アイ, and the pit is like a sunken eye in the ground.
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