"papal edict, highest authoritative document issued by or in the name of a pope," c. 1300, from Medieval Latin bulla "sealed document" (source of Old French bulle, Italian bulla), originally the word for the seal itself, from Latin bulla "round swelling, knob," said ultimately to be from Gaulish, from PIE *beu-, a root supposed to have formed a large group of words meaning "much, great, many," also words associated with swelling, bumps, and blisters (source also of Lithuanian bulė "buttocks," Middle Dutch puyl "bag," also possibly Latin bucca "cheek").

1680s, "stupid;" 1722, "having a bullet-shaped head," from bullet (n.) + -headed.

"hole made by a bullet," 1832, from bullet (n.) + hole (n.).

also bulletproof, "capable of resisting the impact of a bullet," 1816, from bullet (n.) + proof (n.).

"a remedy which is very effective, almost magical;" see silver (adj.) + bullet (n.). The belief in the magical power of silver weapons to conquer foes goes back at least to ancient Greece (as in Delphic Oracle's advice to Philip of Macedon). In Britain, silver bullets as a superstitious countercharm figure in the fictitious Popish Plot (1678).

'Cause champed silver kills stone-dead

Such as are musket-proof 'gainst lead.

[Thomas Ward, from "England's Reformation," 1710]

English folklore beliefs recorded from early 19c. held that a witch could be wounded or revealed (if transformed) only by a wound from a silver bullet. Similar fancies are reported in folk-tales from Ireland and Iceland. The belief in the killing efficacy of silver bullets was transferred to vampires by 1816.