Pronunciation: (bool'u, bul'u),[key] —n., —pl.bul•laePronunciation: (bool'ē, bul'ē).[key] 1. a seal attached to an official document, as a papal bull.
2. an ancient Roman pendant, consisting of a rounded box containing an amulet.
3. Pathol.a large vesicle.
4. Zool.a blisterlike or bubblelike prominence of a bone, as that of the tympanic bone in the skull of certain mammals.