Words hold power. We communicate with them, and as a race, we’re still amazed at them. We inherently think that speaking of something calls upon it and lets it influence us. I’m sure you’ve seen examples of it, such as He Who Must Not Be Named. Thusly, we have euphemisms for words, thinking that if we call it something else it won’t have the same effect. We do it right now with euphemisms for swear words, code words in military communication, politically correct speech, or even double speak.
Where the fun starts is its historical effect on language. Eventually the original word that was avoided falls completely out of use and the euphemism becomes the new word, in a process officially called taboo deformation. One of the most notable examples is the word ‘bear’, which linguistically means ‘brown one’. In fact, the original word for bear is completely lost in our language, and even in the language English came from (combination of Old German and French). We can only infer what it might’ve been by looking at ancient Greek and extrapolating from there. The original word for bear in Proto-Indo European (hypothetical language from which modern languages evolved from) is a synonym for destroyer. From the perspective of a Bronze Age man, a bear is certainly a force of destruction. So calling upon the bear by using its real name was taboo, and remained so for so long, its original name was lost completely.
It’s already been established in fiction where it’s taboo to refer to someone by name, such as Harry Potter’s Voldemort, the true name of the Beast from the Bible, or the big villain of the Guilty Gear video game series (‘that man’). In ancient Egyptian mythology, removing a person’s name from all records was believed to destroy their Ka (roughly speaking, their soul).
Instead, where knowing a name gives the speaker power over the subject, the subject is soo powerful/dangerous that the advantage is reversed. The subject gaining power over the speaker.
Here's a depiction of bears for use in your D&D games, without really changing any rules, so much as giving a story to the larger ones.
Dire Bear
As written in the standard rules for D&D 3.0+, this is the beast that man tried to forget. In times thankfully forgotten, the beast that would later be called bear roamed the lands. It slept like our bears, but its slumber was more akin to dragon sleep than human rest, its cavern a place of prophesied dread for the inevitable stirrings. It walked through the forest like our bears, but the ground shook in terror at its footsteps. Its claws can rend steel, its rage can bring a frost giant to a standstill.
They had been forgotten for so long. But then someone found their name. Some fool found their name and spoke it. Not even most bears remember their nature, but some retain an inkling of something missing. When they hear their name, they remember strength, power, and rage as footpads of creatures forgotten walk the land again.
