You searched for: “adventitia
adventitia (s) (noun)
A membrane that covers an organ but is not part of that organ: "Adventitia is primarily made up of connective tissue."

"The layer known as adventitia is a pliable sheet of tissue that covers, lines, or connects the organs or cells of animals or plants."

This entry is located in the following units: ad- (page 10) -al; -ial, -eal (page 7)