The word nickel derives from the German word Kupfernickel, which translates roughly as “Devil’s copper”. It got that name because once in the Middle Ages, German miners found a large strike of what they thought was pure copper, but turned out to be more of a copper-nickel mixture. This happens more frequently than you might think. (Nickel deposits often seem more like silver, at first.) Nickel wasn’t useless, and there was plenty of copper in the mixture, which made refining the two metals very difficult. The extra work to make their strike economically viable reduced the value of their find, so the miners understandably cursed it, attributing the find to Nick, a mischievous sprite from German mining mythology: Nickel. It’s from this association that in English, the Devil came to be sometimes known as Old Nick.
That old devil, Nickel (artist’s rendering—no photo available).
Refining copper and nickel is a lot easier with modern technology. Nickel is used in a lot of alloys, and sometimes in its pure form. In the United States, the silver half dime coin was discontinued in 1883 and replaced with a physically larger coin that was 75% copper and only 25% nickel, also worth five cents. This new coin, despite being mostly copper, was dubbed the nickel. The design of the coin has changed a few times since 1883, but its metallic composition has remained the same. The Canadian five-cent piece came along later, and it was also called a nickel. This made more sense, since the Canadian piece actually was 99% nickel. It remained that way until 1981, when Canadian nickels adopted the same alloy of the US coin. Canadian nickels today are mostly nickel-plated steel, but no one feels the need to change the name.