1540s, "flesh or meat of the belly" (a sense now obsolete), from Latin abdomen "the belly," a word of unknown origin, Perhaps [OED, Watkins] from abdere "conceal" (from ab "off, away" + PIE root *dhe- "to set, put"), with a sense of "concealment of the viscera," or else "what is concealed" by proper dress. De Vaan, however, finds this derivation "unfounded." Anatomical sense of "part of the mammalian body between the diaphragm and the pelvis" is from 1610s. Zoological sense of "posterior division of the bodies of arthropods" is by 1725.