‖n. [ NL. See Hydro-, and Peritoneum. ] (Med.) Same as Ascites. [ 1913 Webster ]

n. [ L. peritoneum, peritonaeum, Gr. &unr_;, &unr_;, fr. &unr_; to stretch all around or over; peri` around + &unr_; to stretch. ] (Anat.) The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac. [ Written also peritonæum. ] [ 1913 Webster ]

n. [ Pleuro- + peritoneum. ] (Anat.) The pleural and peritoneal membranes, or the membrane lining the body cavity and covering the surface of the inclosed viscera; the peritoneum; -- used especially in the case of those animals in which the body cavity is not divided. [ 1913 Webster ]

☞ Peritoneum is now often used in the sense of pleuroperitoneum, the pleuræ being regarded as a part of the peritoneum, when the body cavity is undivided. [ 1913 Webster ]