Source : Webster's Revised Unabridged Dictionary (1913)

Abdomen \Ab*do"men\, n. [L. abdomen (a word of uncertain
   etymol.): cf. F. abdomen.]
   1. (Anat.) The belly, or that part of the body between the
      thorax and the pelvis. Also, the cavity of the belly,
      which is lined by the peritoneum, and contains the
      stomach, bowels, and other viscera. In man, often
      restricted to the part between the diaphragm and the
      commencement of the pelvis, the remainder being called the
      pelvic cavity.

   2. (Zo["o]l.) The posterior section of the body, behind the
      thorax, in insects, crustaceans, and other Arthropoda.

Source : WordNet®

abdomen
     n 1: the region of the body of a vertebrate between the thorax
          and the pelvis [syn: {venter}, {stomach}, {belly}]
     2: the cavity containing the major viscera; in mammals it is
        separated from the thorax by the diaphragm [syn: {abdominal
        cavity}]