The Collaborative International Dictionary
water jacket \water jacket\ A chamber surrounding a vessel or tube in which water may be circulated, thereby regulating the temperature or supply of heat to the vessel. Used in laboratory and manufacturing equipment.
WordNet
n. a container filled with water that surrounds a machine to cool it; especially that surrounding the cylinder block of an engine
Wikipedia
A water jacket is a water-filled casing surrounding a device, typically a metal sheath having intake and outlet vents to allow water to be pumped through and circulated. The flow of water to an external heating or cooling device allows precise temperature control of the device.
Usage examples of "water jacket".
And the mounting, otherwise identical to that of the '19A4s, was different in one important respect: Traverse of the weapon was restricted only by the length of the hose connecting the water jacket to the water reservoir.
The thick water jacket of the gun swept back and forth, firing a spearhead of flame into the darkness.
The muzzle of the gun glowed cherry red, like a horseshoe fresh from the forge, and the steam from the water jacket whistled shrilly as the coolant boiled.
He frowned, his thoughts drifting toward the land engine, and whether a full water jacket around the condenser would even out the pump's flow.
It was simple, really, consisting of a water jacket, holding about two pints, around a central chimney.