an attached casing holding or circulating water around something to be cooled or kept at a constant temperature, esp. around or through the cylinder head and block of an internal-combustion engine
A casing containing water circulated by a pump, used around a part to be cooled, especially in water-cooled internal-combustion engines.
transitive verbwa·ter-jack·et·ed, wa·ter-jack·et·ing, wa·ter-jack·ets
To encase in or provide with a water jacket.