abdomen (n.) Look up abdomen at Dictionary.com
1540s, "belly fat," from Latin abdomen "belly," of unknown origin, perhaps from abdere "conceal," with a sense of "concealment of the viscera," or else "what is concealed" by proper dress. De Vaan, however, finds this derivation "unfounded." Purely anatomical sense is from 1610s. Zoological sense of "posterior division of the bodies of arthropods" first recorded 1788.