'infect' originates from Latin, specifically the word 'inficere', where the prefix 'in-' meant 'into/onto' and the root 'ficere' (related to 'facere') meant 'to make/do'.

'infect' changed via Late Latin 'infectare' and Old French forms into Middle English (examples: 'infecten', 'infect'), and eventually became the modern English word 'infect'.

Initially, Latin forms often carried senses of 'staining' or 'tainting'; over time in English the sense shifted and narrowed to 'introduce disease or cause to become ill,' which is the current primary meaning.