'explainer' originates from the English word 'explain', which comes from the Latin word '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', from which 'explainer' is derived.

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