(1) The membrane that lines the abdominal cavity and covers most of the abdominal organs. (From the Greek peri- meaning around + tonos meaning a stretching = a stretching around).
(2) (Science: anatomy) 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.
Alternative forms: peritonaeum.
Origin: L. Peritoneum, peritonaeum, Gr, fr. To stretch all around or over; around _ to stretch.