basket trap for fish, placed in the opening of a weir
笱 refers to a specific fishing tool: a basket trap placed at a weir opening to catch fish. Its meaning is narrow and concrete, with no common abstract extensions.
笱 combines 竹 (bamboo) with 句, which likely contributes a phonetic element. The bamboo top suggests the material of the trap, while 句 may have originally been a phonetic component.
The bamboo top 竹 hints at the woven material, and the bottom 句 looks like a hook or opening. Picture a bamboo basket hooked into a weir to trap fish.
For コウ, imagine a fish swimming into the trap and making a surprised 'koh!' sound as it gets caught: koh -> コウ.
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