1. A thin membranous bag in animals, which serves as the receptacle of some secreted fluid, as the urinary bladder, the gall bladder, _c. By way of eminence, the word, in common language, denotes the urinary bladder, either within the animal, or when taken out and inflated with air.

2. Any vesicle, blister or pustule, especially if filled with air, or a thin, watery liquor.

3. In botany, a distended membranaceous pericarp.