food made of crushed and cooked rice
糍 refers to a specific food made from crushed and cooked rice, essentially a rice cake or paste. Its meaning is narrow and concrete, centered on this prepared rice product.
糍 combines 米 (rice) with 兹, which likely contributes the sound. The character is used for a rice-based food, but its detailed historical development is uncertain.
The left side is 米 (rice), and the right side 兹 looks like twisted threads. Imagine crushing rice grains until they become a sticky, twisted mass: that's the crushed and cooked rice food 糍.
For シ, picture a sheaf of rice being crushed into a paste: sheaf -> シ, and the rice becomes the food 糍.
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