The word "unheard" is a straightforward English compound formed by the productive application of the native negative prefix "un-" to the past participle "heard." The prefix "un-" descends from the Proto-Germanic un-, a common negation marker, which itself has roots in the Proto-Indo-European n̥-, meaning "not." The core verb "hear" originates from the Old English hīeran, tracing back to the Proto-Germanic hauzijaną, "to hear," and ultimately to the Proto-Indo-European h₂ḱh₂owsyéti, from the root h₂eḱ-, meaning "sharp" or "pointed," which evolved to signify acute perception. Thus, the literal construction "not heard" logically extends to describe anything from a sound that goes unperceived to an opinion that is ignored or a fact that remains unknown.

Structure: un (not) + heard (perceived by ear) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - heard: The past participle of the verb "hear," from Old English hīeran, of Germanic origin. In this compound, it functions as the core lexical element meaning "perceived by ear."