/ Dictionary / Index A adventitia: Meaning and Definition of Find definitions for: ad•ven•ti•ti•a Pronunciation: (ad"ven-tish'ē-u, -tish'u), [key] — n. Anat. the external covering of an organ or other structure, derived from connective tissue, esp. the external covering of a blood vessel. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: adventitia (Thesaurus) Adventist adventitious Related Content Daily Word Quiz: inutiae Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language