This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 汫 is uncertain. It combines 氵 (water) with 井 (well), but the original meaning and formation are unclear.
The left side is water 氵 and the right side is a well 井. Picture a well filled with water, but since the meaning is uncertain, treat this as a visual placeholder.
For ケイ, imagine a well (井) with a water (氵) bucket shaped like the letter K: K -> ケイ, and the bucket is lowered into the well.
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