to increase five-fold
蓰 centers on multiplying by five: to increase something five-fold. It is a specific numerical intensifier rather than a general growth term.
蓰 combines 艹 (grass/plant) with 徙, which likely contributes the sound and the idea of moving or shifting. The exact historical development of the 'five-fold' meaning is uncertain.
The grass top 艹 sits above 徙, like a plant that multiplies its shoots five times over. Picture a patch of grass that suddenly grows five times thicker.
For シ, imagine a sheaf of grass that has increased five-fold: sheaf -> シ, and the grass top 艹 reminds you of the plant connection.
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