The posterior segment of the body in arthropods.Origin of abdomen Latin abd??men, belly; see dh??- in Indo-European roots. abdomen Noun (plural abdomens or abdomina)(anatomy) The belly, or that part of the body between the thorax and the pelvis, not including the back; or in some lower vertebrates, the portion between the cardiac and caudal regions. [First attested in the early 17th century.] (ana