measuring box, (kokuji)
桝 centers on a container for measuring volume, specifically a traditional wooden measuring box. It is a kokuji created in Japan for this purpose.
桝 is a kokuji, a kanji created in Japan. It combines 木 (wood) with 舛, which here likely represents a container or measuring vessel, to express a wooden measuring box.
The left side is wood 木, and the right side 舛 looks like a box with a lid and a handle. Picture a wooden box used for measuring rice or sake.
For ます, imagine a wooden measuring box filled with rice, and you say 'mass' of rice: mass -> ます, because the box holds a mass of grains.
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