Sentence:  Temperatures of the shield and of the surface of the water cooled anode holder were measured by thermocouples to account for heat received by the <WSD>coolant</WSD> but not originating from the anode plug . 
Meaning of the word marked with <WSD> tags:  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