The word "unbeknown" is a relatively modern English formation, coined in the 17th century by combining established Germanic elements. The core is the past participle "known," from the ancient Proto-Germanic verb meaning "to recognize." The prefix "be-" was added, a common intensifier in older English, to create the archaic form "beknown," meaning "known about." Finally, the negative prefix "un-" was attached, resulting in the literal sense of "not known about." The logic of its construction is transparent: it directly builds the meaning of "without the knowledge (of someone)" from its three constituent parts, preserving a formal and slightly archaic tone.

Structure: un (not) + be (about, by) + known (known) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - be: A prefix of Germanic origin (Old English be-, bi-), meaning "about, around, by." In this word, it functions as an intensifier or to give a sense of "by." - known: The past participle form of the verb "know," from Old English cnāwan, meaning "to perceive, recognize." It functions as the core lexical root.