From fat + buttock + -ed.
fat-buttocked
- (rare) Steatopygous, big-buttocked.
2003, Alys Clare, Fortune like the Moon[1], →ISBN:Gluttony, rotund and fat-buttocked, was upturned into a barrel of excrement; Anger, face contorted with rage and agony, had his skull prised open and his brains sucked out by hunchbacked devils.
2007, Paul Morris“, Roasting the Pig: A Vision of Cluny, Cockaigne and the Treatise of Garcia of Toledo[2], →ISBN:Indeed, he transforms his superior into the very personification of gluttony: “... he was fat, oily, refined, rotund, heavy, ponderous, weighty, massive, cyclopean, a giant in body, broad-chested, deep-bellied, fat-buttocked, his eyes set wide apart, with a jutting forehead, a ferocious countenance, commanding of respect, with a good shock of hair and a bull-neck.”