The word 'unreturned' is a modern English formation built upon the well-established verb 'return.' The verb itself has a journey from Latin 'retornare' (to turn back), through Old French, into Middle English. By adding the native Germanic negative prefix 'un-' to the past participle 'returned,' the word is logically constructed to mean "not having been turned back." This literal sense of not coming back evolved to describe objects not sent back, such as library books, and abstractly, feelings or favors not reciprocated. The logic is transparent: the state (ed) of not (un) having been returned.

Structure: un (not) + return (go back) + ed (adjective suffix) - un: A prefix of Germanic origin (Old English 'un-'), meaning "not," used to form negatives. - return: A verb from Old French 'retorner,' itself from Latin 're-' (back) + 'tornare' (to turn). Its core sense is "to turn back." - ed: A suffix of Germanic origin (Old English '-ed', '-od'), commonly used to form past participles which can function as adjectives.