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

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

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