'explain' originates from Latin, specifically the word 'explanare,' where 'ex-' meant 'out' and 'planare' meant 'to make plain or flat.'

'explanare' transformed into the Old French word 'esplaner,' and eventually became the modern English word 'explain' through Middle English.

Initially, it meant 'to make plain or clear,' and this meaning has largely remained the same in modern usage.