whip, cane, wooden writing slate
笘 centers on a long, thin object made from bamboo: a whip, a cane, or a wooden writing slate. The common thread is a bamboo strip used as a tool for striking or writing.
笘 combines 竹 (bamboo) with 占, which likely contributes a phonetic element. The character originally referred to a bamboo whip or a bamboo writing tablet.
The bamboo top 竹 over 占 suggests a bamboo strip used for divination or record-keeping, like a wooden writing slate, or as a tool for discipline, like a whip or cane.
For セン, imagine a bamboo cane used by a strict sensei (先生, せんせい) to whip students: セン from せんせい, and the bamboo cane is the tool.
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