bamboo tube or pipe, fish hook
筩 centers on a hollow bamboo object: a tube or pipe made from bamboo. The fish hook sense is a specific application of a bamboo tube used as a fishing tool.
筩 combines 竹 (bamboo) with 甬, which likely contributes the sound and suggests a hollow passage, giving the idea of a bamboo tube or pipe.
Bamboo 竹 on top of 甬, which looks like a hollow tube with a cap. Picture a bamboo stalk cut into a pipe or a fishing rod with a hook.
For トウ, imagine a bamboo tube used as a toe ring: toe -> トウ, and the hollow bamboo pipe fits snugly.
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