I read once that the root word that evolved into all the modern Indo-European variants of bear began as a euphemism to avoid having to say the creature’s name and risking summoning it. It meant something like “the brown one.”
In English, and other Germanic language, it comes from the brown one. In Slavic languages bears are called honey eaters. In other languages though like Welsh they don't appear to have had the taboo and use a deririvative of the older PIE word, which is thought to be something like rktho.
