The rounded part of your rear end, made mostly of muscle and fat.
From Old English 'buttuc' (a thick piece or knob). Related to 'butt' (the end of something). The word originally referred to any blunt or rounded thing, then specifically to this body part.
Humans have disproportionately large buttocks compared to other primates—this evolved as we became bipedal, and we actually use these muscles constantly to stay upright, making them some of your most powerful muscles.
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