bulla

Concise Oxford English Dictionary © 2008 Oxford University Press:
bulla /ˈbʊlə/

▶noun (pl. bullae /ˈbʊliː/)

• 1 Medicine a large blister or other cavity containing fluid or air.

• 2 Anatomy a rounded prominence.

• 3 a round seal attached to a papal bull.

– derivatives
bullate adjective (Botany),
bullous adjective (Medicine).

– origin L., lit. ‘bubble’.