a fluid agent (gas or liquid) that produces cooling; especially one used to cool a system by transferring heat away from one part to another
"he added more coolant to the car's radiator"
"the atomic reactor used a gas coolant"
"lathe operators use an emulsion of oil and water as a coolant for the cutting tool"
A medium, usually fluid, used to draw heat from an object.
"The mechanic drained the old coolant and replaced it with fresh antifreeze to help the engine run cooler during the summer drive."