Definition of "bulla"

(biology, medicine) A blister, vesicle, or other thin-walled cavity or lesion, as:

1. (biology, medicine) (usually and especially) Such a blister that is more than 5 mm in diameter.

(archaeology) A clay envelope or hollow ball, typically with seal impressions or writing on its outside indicating its contents.

(historical) In ancient Rome, a kind of amulet or boss.

Later, a handwritten document from the papal chancellery.  examples

The tympanic part of a temporal bone (having a bubble-like appearance)  examples

A rich Jamaican cake made with molasses and spiced with ginger and nutmeg.  examples