a substance, usually a fluid, that undergoes changes in pressure, temperature, volume, or form as part of a process for accomplishing work.
Everyday English Words With Ancient Arabic RootsThroughout the English language are Arabic roots. Read on for the surprising Arabian delights in English. English would be awfully bland without them.
Origin of working substance
First recorded in 1895–1900
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for working substance
the fluid, esp water, steam, or compressed air, that operates an engine, refrigerator, etc
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