Many cultures hold "real" names as being special in some way. One could talk about the power of the names, but more importantly, it is common for people to regard it as disrespectful to mention the true name of something in its presence. And beings disrespectful in the presence of something powerful could have very real, dangerous consequences. This resulted in pairs of "noa" and "taboo" names. Anthropologists often use the Polynesian terms of noa (allowed) and tabu/taboo (forbidden) because the island people of the Pacific provide excellent examples of how the widest possible array of actions could come under complicated rules of prohibition. Indeed, the Polynesian example is so well-known that the word “taboo” has found its way into common English usage. In many cases - including in Europe - the prohibition about name use had more to do with respect than power.

The following is an excerpt from my Introduction to Folklore dealing with this:

Specifically naming certain mountains, animals, supernatural beings, and other things could be prohibited, particularly in their presence. Various cultures have consequently provided a range of noa names for various things. Anthropologists also refer to these alternative means of address as circumlocutions. A noa name is used under circumstances when the actual name would be taboo. Northern European bakers avoided naming the fire, but instead spoke of the heat. Butchers would not refer to blood. They replaced that word with “sweat.”

The English word “bear” descends from the Proto-Germanic root *beron meaning “brown one.” This was apparently a way of avoiding the original word *rkto, from which was related to the Latin ursus. In this case, prehistoric speakers of ancestral English presumably avoided the actual name until it ceased to be remembered. Ethnographic evidence from the northern latitudes indicate that one should not name the bear in its presence (that is, in the forest) or when planning to hunt for a bear. Compare, for example, Russian medved, which means honey eater, and Swedish sotfot, meaning “sweet foot.” Both refer to the bear’s interest in honey. Native American Shoshoni politely discuss the bear as “our father’s sister.”

Words applied to the supernatural beings of nature provide what appear to be additional examples of circumlocution, which are particularly pertinent for a discussion of folklore. The English word “elf” descends from a root word that apparently described a shimmering, shiny appearance. It is related to the name Alps, the Swiss mountains, and the River Elbe in Germany. Because the term “elf” originally referred to a characteristic of the supernatural beings as opposed to what had been an actual, presumably-taboo name, it would be easy to assume that this term is a circumlocution. It is possible, however, that there never was a proper name for these supernatural beings, who were simply discussed in polite, descriptive ways. Eventually, however, people forgot the original meaning of the term “elf,” and as it became regarded as a proper name, various other circumlocutions including the “good neighbors” or the “fair folk” became alternatives safer than saying “elf.”

Similar circumlocutions are found elsewhere, Scandinavian elves are often called hulderfolk or simply huldre, meaning the “hidden folk” or the “hidden ones.” The Irish word for fairies, sidhe (hence, for example, banshee – woman fairy), was once a noa name that made reference to living in a mound. But again, there may have been no taboo, proper name that was being avoided. Centuries of use have made the term sidhe sacred, and it is now avoided. Instead the Irish may speak of the “wee folk” or the “beautiful ones.” Each culture can have a range of contrasting noa and taboo words, even if there are only linguistic remnants of this practice.