urosome

from The Century Dictionary.

• noun In certain crustaceans, as the amphipods, the last three segments of the pleon or abdomen. Compare mesosome and metasome.
• noun In biology: The last morphological segment of the tail; the terminal somatome of a vertebrate. See gephyrocercal.
• noun The post-thoracic region of the body of arthropods; the abdomen or postabdomen as distinguished from the cephalothorax, and as composed of a series of urosomites or uromeres.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) The abdomen, or post-abdomen, of arthropods.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun zoology The abdomen or postabdomen of an arthropod.