steep slope
壗 centers on a steep slope or incline, describing a sharply rising or falling piece of ground.
壗 combines the earth radical 土 with the phonetic component 盡, suggesting a steep earthen slope. The exact historical development is uncertain.
The left side 土 (earth) and the right side 盡 (which looks like a complex stack) together suggest a steep earthen slope: imagine a towering pile of earth that forms a sharp incline.
For まま, picture a steep slope that a mother (まま, mama) carefully climbs while carrying her child: mama -> まま, and the steep earth slope makes the climb difficult.
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