(1):

(n.) A bleb; a vesicle, or an elevation of the cuticle, containing a transparent watery fluid.

(2):

(n.) The ovoid prominence below the opening of the ear in the skulls of many animals; as, the tympanic or auditory bulla.

(3):

(n.) A genus of marine shells. See Bubble shell.

(4):

(n.) 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.