"backside" in the noun sense
1. rear, backside, back end
the side of an object that is opposite its front
"his room was toward the rear of the hotel"
2. buttocks, nates, arse, butt, backside, bum, buns, can, fundament, hindquarters, hind end, keister, posterior, prat, rear, rear end, rump, stern, seat, tail, tail end, tooshie, tush, bottom, behind, derriere, fanny, ass
the fleshy part of the human body that you sit on
"he deserves a good kick in the butt"
"are you going to sit on your fanny and do nothing?"
Source: WordNet® (An amazing lexical database of English)
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