Anatomy Any of various distensible membranous sacs, such as the urinary bladder or the swim bladder, that serve as receptacles for fluid or gas.
An item resembling one of the membranous sacs in animals: the bladder of a football.
Botany Any of various hollow or inflated saclike organs or structures, such as the floats of certain seaweeds or the specialized traps of bladderworts.
Pathology A blister, pustule, or cyst filled with fluid or air; a vesicle.