fun·da·ment 
(fŭndə-mənt)
(fŭndə-mənt)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).
[Middle English foundement, from Old French fondement, from Latin fundāmentum, from fundāre, to lay the foundation, from fundus, bottom.]