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A casing containing water circulated by a pump, used around a part to be cooled, especially in water-cooled internal-combustion engines.
(Mechanical Engineering) a water-filled envelope or container surrounding a machine, engine, or part for cooling purposes, esp the casing around the cylinder block of a pump or internal-combustion engine. Compare air jacket
a water-filled casing or compartment used to water-cool something, as an engine or machine gun.