The Collaborative International Dictionary
Pleuroperitoneum \Pleu`ro*per`i*to*ne"um\, 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.
Note: Peritoneum is now often used in the sense of pleuroperitoneum, the pleur[ae] being regarded as a part of the peritoneum, when the body cavity is undivided.
Wiktionary
n. (context anatomy English) The pleural and peritoneal membranes, or the membrane lining the body cavity and covering the surface of the enclosed viscera; the peritoneum; used especially in the case of those animals in which the body cavity is not divided.