'reagent' originates from Latin, specifically the word 'reagere,' where 're-' meant 'again' and 'agere' meant 'to act.'

'reagere' transformed into the French word 'réagir,' and eventually became the modern English word 'reagent' through Middle English.

Initially, it meant 'to act again,' but over time it evolved into its current meaning of 'a substance used in chemical reactions.'