noun Date: 1855 a usually fluid substance that through changes of temperature, volume, and pressure is the means of carrying out thermodynamic processes or cycles (as in a heat engine)
WORKING SUBSTANCE
Meaning of WORKING SUBSTANCE in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012