Noun
a formal proclamation issued by the pope (usually written in antiquated characters and sealed with a leaden bulla)
Source: WordNetJedin 79–82 Occasion, sessions, and attendance The Council, depicted by Pasquale Cati (Cati da Iesi) In reply to the Papal bull Exsurge Domine of Pope Leo X (1520), Martin Luther burned the document and appealed for a general council. Source: Internet
In 1483 a Papal bull decreed that the islands would be neutral during time of war. Source: Internet