A kobold (German: [ˈkoːbɔlt]; kobolt, kobolde, cobold) is a general or generic name for the household spirit (hausgeist) in German folklore.
It may invisibly make noises (i.e., be a poltergeist), or helpfully perform kitchen chores or stable work. But it can be a prankster as well. It may accept a bribe or offering of milk, etc. for its efforts or good behaviour. When mistreated (cf. fig. right), its reprisal can be utterly cruel.
A goblin is a small, grotesque, monstrous humanoid creature that appears in the folklore of multiple European cultures. First attested in stories from the Middle Ages, they are ascribed conflicting abilities, temperaments, and appearances depending on the story and country of origin, ranging from mischievous household spirits to malicious, bestial thieves. They often have magical abilities similar to a fairy or demon, such as the ability to shapeshift.
Similar creatures include brownies, dwarves, duendes, gnomes, imps, leprechauns, and kobolds, but it is also commonly used as a blanket term for all small, fay creatures. The term is sometimes expanded to include goblin-like creatures of other cultures, such as the pukwudgie, dokkaebi, or ifrit.
Cobalt is a chemical element; it has symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, somewhat brittle, gray metal.
Cobalt-based blue pigments (cobalt blue) have been used since antiquity for jewelry and paints, and to impart a distinctive blue tint to glass. The color was long thought to be due to the metal bismuth. Miners had long used the name kobold ore (German for goblin ore) for some of the blue pigment-producing minerals. They were so named because they were poor in known metals and gave off poisonous arsenic-containing fumes when smelted. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), which was ultimately named for the kobold.