smear, slander, defile
衊 centers on staining or dirtying something, whether physically by smearing or metaphorically by slandering or defiling a reputation.
衊 combines 血 (blood) with 蔑 (disdain, slight), suggesting the idea of staining or defiling with blood or disgrace. The exact historical development is uncertain.
Blood 血 and disdain 蔑 together create a scene of smearing blood to defile or slander someone.
For ベツ, imagine a messy smear of blood that looks like a red 'Bets' stain: Bets -> ベツ.
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