a membranous sac closely connected by various ducts to the liver, in which excess gall, or bile, is stored and concentrated
See gallbladder in American Heritage Dictionary 4
also gall bladder(gôlˈblădˌər)
noun
A small, pear-shaped muscular sac, located under the right lobe of the liver, in which bile secreted by the liver is stored until needed by the body for digestion.