'explanatory' originates from Latin, specifically the word 'explanatorius,' where 'ex-' meant 'out' and 'planare' meant 'to make plain.'

'explanatorius' transformed into the French word 'explanatoire,' and eventually became the modern English word 'explanatory' through Middle English.

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