The word "undimmed" is a relatively modern English formation, built upon the ancient Germanic root for darkness. The core adjective "dim," with Proto-Germanic origins meaning "dark" or "faint," was verbed to mean "to make dark or faint." Adding the Old English negative prefix "un-," one of the most fundamental and persistent in the language, directly reverses the action, creating a term that literally means "not made faint." This logical construction elegantly conveys the abstract sense of something retaining its full brilliance, vigor, or clarity without any reduction, whether applied to literal light or metaphorical qualities like enthusiasm or memory.

Structure: un (not) + dimmed (made less bright) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative or reversing particle. - dimmed: The past participle form of the verb "dim," from Old English dim or dimm, meaning "dark, gloomy, faint." In this structure, it functions as the core adjective meaning "made less bright."