noun a genus of marine shells. ·see bubble shell.
2. bulla ·noun a bleb; a vesicle, or an elevation of the cuticle, containing a transparent watery fluid.
3. bulla ·noun the ovoid prominence below the opening of the ear in the skulls of many animals; as, the tympanic or auditory bulla.
4. bulla ·noun a leaden seal for a document; ·esp. the round leaden seal attached to the papal bulls, which has on one side a representation of st. peter and st. paul, and on the other the name of the pope who uses it.