'non-infectious' originates from the prefix 'non-' meaning 'not' and the word 'infectious' which comes from Latin 'infectiosus', meaning 'to taint or corrupt'.

'infectiosus' transformed into the Old French word 'infectieux', and eventually became the modern English word 'infectious'. The prefix 'non-' was added to denote the opposite meaning.

Initially, 'infectious' meant 'to taint or corrupt', but over time it evolved into its current meaning of 'capable of causing infection'. Adding 'non-' negates this meaning.