what is adventitia
adventitia. n. 1. (Anatomy) the outermost covering of an organ or part, esp the outer coat of a blood vessel. [C19: New Latin, from the neuter plural of Latin adventÄ«cius; see adventitious].dventitia. n. 1. (Anatomy) the outermost covering of an organ or part, esp the outer coat of a blood vessel. [C19: New Latin, from the neuter plural of Latin adventÄ«cius; see adventitious].