This radical has actually the meaning: corpse 尸. But due to its use in tail 尾, urine 尿, or flatulence 屁, it is considered to generally mean 'buttocks'.
Variant of hill 丘. Clan families often had their estates on the top of hills. This developed into the family name. It can be seen as one person 人, which is modified as: 厂 and a “plus +” as a multiplier, so that many persons form a family.
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