Open English Wordnet
Nouns
(n)basis, base, foundation, fundament, groundwork, cornerstonethe fundamental assumptions from which something is begun or developed or calculated or explained“the whole argument rested on a basis of conjecture”
(n)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, assthe 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?”
(n)foundation, base, fundament, foot, groundwork, substructure, understructurelowest support of a structure“it was built on a base of solid rock”, “he stood at the foot of the tower”