n. An underground conduit for drainage; a common sewer: as, the cloaca maxima at Rome.n. A sink; a privy.n. [NL.] In zoology: In vertebrates, the enlarged termination of the rectum or lower bowel, forming a cavity originally in common with that of the allantois (in those animals which have an allantois) and permanently in common with the termination of the urogenital organs; the common chamber into which the intestine, ureters, sperm-ducts, and oviducts open, in sundry fishes, in reptiles and birds, and in the ornithodelphous mammals.n. In invertebrates, the homologous or analogous and corresponding structure effecting sewerage of the body: as in sponges, the common cavity in which the interstitial canal-systems open; in holothurians, the respiratory tree (which see, under respiratory).n. In entomology: A cavity found in many insects at the end of the abdomen, between the last dorsal and ventral segments, and receiving the extremity of the rectum. Also called the rectogenital chamber. The cæcum, or dilatation of the posterior end of the intestine.n. In ascidians, the common central cavity into which open the atrial chambers of all the ascidiozooids of an ascidiarium.n. [NL.] In pathology: In cases of necrosis, the opening in the sound bone which leads to the inclosed dead bone.n. The union of rectum, bladder, and organs of generation in a common outlet: a malformation resulting from arrest of development.