'irradiate' originates from Latin, specifically the word 'irradiatus,' where 'in-' meant 'into' and 'radius' meant 'ray.'

'irradiatus' transformed into the French word 'irradiate,' and eventually became the modern English word 'irradiate' through Middle English.

Initially, it meant 'to shine light upon,' but over time it evolved into its current meanings of 'expose to radiation' and 'illuminate.'