Kupfernickel.

From Kupfer (“copper”) + Nickel (“mischievous spirit or demon”). This word originated as a pejorative German term for ores of the element nickel, whose bright green color closely resembles malachite, an otherwise reliable indicator of valuable copper ore. However, like iron, nickel ore is impossible to smelt at the relatively low temperatures needed to smelt copper. (This is also why the Copper Age preceded the Iron Age.) Annoyed at wasting their time on such ore, German miners began calling it cupfernickel, that is, "copper demon." When chemists eventually identified and named the element in the ore, they shortened the name of the ore to nickel. The name of this element thus has the same roots as the phrase "Old Nick," which refers to a supreme devil or demon. Feeling a bit whimsical, chemists of that same period named another newly isolated iron-like element, cobalt, after a mischievous German household spirit, the "kobold".