fly which is used similarly to cantharides
蝥 refers to a type of fly used similarly to cantharides (blister beetles), likely for medicinal or irritant purposes. Its meaning is narrow and technical.
蝥 combines 虫 (insect) with 敄, which likely provides the sound. The character denotes a specific insect, but the exact historical development of 敄 is uncertain.
The top part 敄 looks like a spear (矛) with an action hand (攵), and the bottom is 虫 (insect). Imagine a spear-wielding hand hunting a fly that is used like a blister beetle.
For ボウ, picture a bow (ボウ) being used to swat the fly: bow -> ボウ, and the fly is the target.
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