THAT is what high tension wires are?! I've always seen it in the context of the massive transmission lines, so I thought it meant that the wires themselves were under high tension from their weight.

I was today years old when I learned...

Similarly, I thought it meant because they were stretched to high tension to avoid sagging as much.

Also "high tension power lines," which being heavy catenaries presumably are in high mechanical tension, but must surely have gotten that name from the voltage = tension thing.

German has this too: voltage = Spannung = tension.

This must go right back to the earliest writings on voltage as a concept.

French also has "tension" in this very sense.

https://fr.wikipedia.org/wiki/Tension_%C3%A9lectrique