coolant

UK: /ˈkuːlənt/ US: /ˈkulənt/ ,(ko̅o̅′lənt)

WordReference Random House Learner's Dictionary of American English © 2025

cool•ant /ˈkulənt/   n. 

1. Thermodynamics a substance used to reduce the temperature of a system below a certain value:
   [countable] coolants made from alcohol mixtures.
   [uncountable] Coolant had spilled over the engine.

WordReference Random House Unabridged Dictionary of American English © 2025

cool•ant  (ko̅o̅′lənt), n. 

1. Physics, Thermodynamics a substance, usually a liquid or a gas, used to reduce the temperature of a system below a specified value by conducting away the heat produced in the operation of the system, as the liquid in an automobile cooling system or the fluid that removes heat from the core of a nuclear reactor.
2. Thermodynamics a lubricant that dissipates the heat caused by friction.

• cool + -ant 1925–30

Collins Concise English Dictionary © HarperCollins Publishers::

coolant / ˈkuːlənt/ noun

1. a fluid used to cool a system or to transfer heat from one part of it to another
2. a liquid, such as an emulsion of oil, water, and soft soap, used to lubricate and cool the workpiece and cutting tool during machining