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working substance

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noun
  1. a substance, usually a fluid, that undergoes changes in pressure, temperature, volume, or form as part of a process for accomplishing work.

Origin of working substance

First recorded in 1895–1900
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for working substance

working substance

working fluid

noun
  1. 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