/ Dictionary / Index M mesothelium: Meaning and Definition of Find definitions for: mes•o•the•li•um Pronunciation: (mez"u-thē'lē-um, mes"-, mē"zu-, -su-), [key] — pl. -li•a epithelium of mesodermal origin, which lines the body cavities. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: mesothelium (Thesaurus) mesothelioma mesothorax Related Content Daily Word Quiz: placid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language