bladder Definition

bladder
noun

1. anatomy.
In all mammals, and some fish, amphibians and reptiles: a hollow sac-shaped organ with a thin muscular wall, in which urine produced by the kidneys is stored before it is discharged from the body.
2. Any of various similar hollow organs in which liquid or gas is stored, eg the gall bladder of animals, or the swim bladder of bony fish.
3. A hollow bag made eg of leather, which can be stretched by filling it with air or liquid.
4. In certain plants: a hollow sac-like structure, especially one of the air-filled sacs at the tips of the fronds of bladder wrack.

Etymology: Anglo-Saxon blædre blister or pimple.