the word 'unexplained' is a modern english formation built upon the verb 'explain.' 'explain' entered english from latin 'explanare,' meaning to make plain or flatten out, metaphorically to make clear. the prefix 'ex-' intensifies this action of bringing something out into the open. the negative prefix 'un-,' of old english origin, is then attached to the past participle 'explained' to create an adjective describing a state where something has not been brought out or made clear. thus, the literal sense of "not made flat/clear from within" evolved into the abstract meaning of lacking a known reason or justification.

Structure: un (not) + ex (out) + plained (made clear) - un: a prefix of germanic origin (old english) meaning "not," used to form negatives. - ex: a latin prefix meaning "out of, from, thoroughly." - plained: derived from the past participle of the verb 'explain,' which itself comes from latin 'explanare' (to make level or clear). the root 'plain' relates to making something flat or clear.