'adiactinic' originates from Greek, specifically the word 'aktinos,' where 'a-' meant 'not' and 'aktinos' meant 'ray.'

'aktinos' transformed into the French word 'actinique,' and eventually became the modern English word 'adiactinic' through scientific terminology.

Initially, it meant 'not allowing rays to pass through,' and this meaning has largely remained the same in modern usage.