/ Dictionary / Index P peritoneum: Meaning and Definition of Find definitions for: per•i•to•ne•um Pronunciation: (per"i-tn-ē'um), [key] — pl. -to•ne•ums, -to•ne•a the serous membrane lining the abdominal cavity and investing its viscera. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: peritoneum (Thesaurus) peritonealize peritonitis Related Content Daily Word Quiz: feline Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language