hindquarters

noun

1. the fleshy part of the human body that you sit on

   noun.body

   Synonyms arse ass backside behind bottom bum buns butt buttocks can derriere fanny fundament hind end keister nates posterior prat rear rear end rump

   Source: WordNet 3.0

2. the part of an animal that corresponds to the human buttocks

   noun.animal

   Synonyms croup croupe rump

   Source: WordNet 3.0