bulla

noun (plural bullae /ˈbo͝olē/)

• 1 Medicine a bubblelike cavity filled with air or fluid, in particular.
• a large blister containing serous fluid.
• an abnormal air-filled cavity in the lung.

  [ early 19th century]

• 2 Anatomy a rounded prominence.

  [ mid 19th century]

• 3a round seal attached to a papal bull, typically made of lead.

  [ Middle English]