fundament

fun·da·ment  (fnd-mnt)

n.

1.

a. The buttocks.

b. The anus.

2. The natural features of a land surface unaltered by humans.

3. A foundation, as of a building.

4. An underlying theoretical basis or principle: "All neighbor states ... must revise ... their policy fundaments" C.L. Sulzberger.

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[Middle English foundement, from Old French fondement, from Latin fundmentum, from fundre, to lay the foundation, from fundus, bottom.]

Thesaurus

Noun	1.	fundament - the fundamental assumptions from which something is begun or developed or calculated or explained; "the whole argument rested on a basis of conjecture" cornerstone, groundwork, basis, foundation, base explanation - thought that makes something comprehensible meat and potatoes - the fundamental part; "successful negotiation is the meat and potatoes of arbitration" supposal, supposition, assumption - a hypothesis that is taken for granted; "any society is built upon certain assumptions"
	2.	fundament - 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?" arse, ass, behind, buns, buttocks, derriere, fanny, hind end, hindquarters, keister, nates, posterior, prat, rear end, tooshie, tush, seat, backside, bottom, stern, rump, tail end, tail, bum, can, butt, rear body part - any part of an organism such as an organ or extremity torso, trunk, body - the body excluding the head and neck and limbs; "they moved their arms and legs and bodies"
	3.	fundament - lowest support of a structure; "it was built on a base of solid rock"; "he stood at the foot of the tower" understructure, base, groundwork, substructure, foundation, foot bed - a foundation of earth or rock supporting a road or railroad track; "the track bed had washed away" raft foundation - a foundation (usually on soft ground) consisting of an extended layer of reinforced concrete structure, construction - a thing constructed; a complex entity constructed of many parts; "the structure consisted of a series of arches"; "she wore her hair in an amazing construction of whirls and ribbons" support - supporting structure that holds up or provides a foundation; "the statue stood on a marble support"