a casing, as on the cylinder of a steam engine, filled with live steam to keep the interior hot.
Origin of steam jacket
First recorded in 1830–40
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
engineering a jacket containing steam that surrounds and heats a cylinder
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012