'illustrate' originates from Latin, specifically the word 'illustratus,' where 'in-' meant 'into' and 'lustrare' meant 'to light up.'

'illustratus' transformed into the French word 'illustrer,' and eventually became the modern English word 'illustrate' through Middle English.

Initially, it meant 'to light up or make bright,' but over time it evolved into its current meaning of 'to explain or decorate with pictures.'