'decay' originates from Old French, specifically the word 'decaïr,' where 'de-' meant 'down' and 'caïr' meant 'to fall.'

'decaïr' transformed into the Middle English word 'decayen,' and eventually became the modern English word 'decay.'

Initially, it meant 'to fall down or decline,' but over time it evolved into its current meaning of 'to rot or decompose.'