Gallbladder

n. sac attached to the liver in which bile is stored

The gallbladder (or cholecyst, sometimes gall bladder) is a pear-shaped organ that stores about 50 ml of bile (or "gall") until the body needs it for digestion.
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Gallbladder /gall·blad·der/ the reservoir for bile on the posteroinferior surface of the liver. gall·blad·der or gall bladder n. [more]Gallbladder - Community and Resources

Noun
1. a muscular sac attached to the liver that secretes bile and stores it until needed for digestion
(hypernym) bladder, vesica
(part-holonym) thorax, chest, pectus

A pear-shaped organ that stores bile. It is located below the liver.