'unexplained' originates from the prefix 'un-' meaning 'not' and the word 'explained' from Latin 'explanare', where 'ex-' meant 'out' and 'planare' meant 'to make plain or clear.'

'explanare' transformed into the Old French word 'expliquer,' and eventually became the modern English word 'explain' through Middle English, with 'unexplained' forming by adding the prefix 'un-' to 'explained.'

Initially, 'explain' meant 'to make plain or clear,' and 'unexplained' has retained the meaning of 'not made plain or clear.'