Definition of: peritoneum

(per′ə·tə·nē′əm) noun plural ·ne·a (-nē′ə) Anat.
A serous membrane that lines the abdominal cavity in mammals and is reflected as a more or less complete investment over the viscera. In the higher vertebrates the peritoneum forms a completely closed sac, except in females, where the Fallopian tubes open into the cavity. Also per′i·to·nae′um. [<LL peritonaeum <Gk. peritonaion <peritonos stretched round <peri- around + teinein stretch]
—per′i·to·ne′al or ·nae′al adjective