streams running underground, flowing water
巠 centers on water flowing in a hidden or underground channel, like a subterranean stream. The given meanings both point to this idea of water moving beneath the surface.
巠 is a rare character. It visually combines 一 (one/ground) over 巛 (river) over 工 (work), which may suggest a river channeled or worked underground, but the exact historical development is uncertain.
Picture a single line (一) representing the ground surface, with a winding river (巛) flowing beneath it, and a man-made structure (工) reinforcing the underground channel. This is water flowing secretly underground.
For ケイ, imagine a hidden underground stream that is the key (ケイ) to a secret water supply. The key unlocks the flowing water: key -> ケイ.
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