1. a transparent membrane that lines the abdominal cavity in mammals and covers most of the viscera;
The Collaborative International Dictionary of English v.0.48:
Peritoneum \Per`i*to*ne"um\, n. [L. peritoneum, peritonaeum, Gr.
?, ?, fr. ? to stretch all around or over; peri` around + ?
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 periton[ae]um.]
WordNet (r) 3.0 (2006):
n 1: a transparent membrane that lines the abdominal cavity in
mammals and covers most of the viscera