/ Dictionary / Index P perithelium: Meaning and Definition of Find definitions for: per•i•the•li•um Pronunciation: (per"u-thē'lē-um), [key] — pl. -li•a the connective tissue surrounding certain small vessels, as capillaries. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: perithelium (Thesaurus) perithecium peritonealize Related Content Daily Word Quiz: rustic Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language