'infectious' originates from Latin, specifically the word 'infectiosus,' where 'in-' meant 'into' and 'facere' meant 'to make.'

'infectiosus' transformed into the Old French word 'infectieux,' and eventually became the modern English word 'infectious' through Middle English.

Initially, it meant 'to make unclean or tainted,' but over time it evolved into its current meaning of 'capable of causing infection or disease.'