'reflex' originates from Latin, specifically the word 'reflexus,' where 're-' meant 'back' and 'flectere' meant 'to bend.'

'reflexus' transformed into the French word 'réflexe,' and eventually became the modern English word 'reflex' through Middle English.

Initially, it meant 'bent back,' but over time it evolved into its current meaning of 'an automatic response to a stimulus.'