The Collaborative International Dictionary of English v.0.48:

Fundament \Fun"da*ment\, n. [OE. fundament, fundement,
   fondement, OF. fundement, fondement, F. fondement, fr. L.
   fundamentum foundation, fr. fundare to lay the bottom, to
   found, fr. fundus bottom. See Fund.]
   1. Foundation. [Obs.] --Chaucer.
      [1913 Webster]

   2. The part of the body on which one sits; the buttocks;
      specifically (Anat.), the anus. --Hume.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fundament
    n 1: the fundamental assumptions from which something is begun
         or developed or calculated or explained; "the whole
         argument rested on a basis of conjecture" [syn: basis,
         base, foundation, fundament, groundwork,
         cornerstone]
    2: 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?" [syn: 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, ass]
    3: lowest support of a structure; "it was built on a base of
       solid rock"; "he stood at the foot of the tower" [syn:
       foundation, base, fundament, foot, groundwork,
       substructure, understructure]