'infidel' originates from Latin, specifically the word 'infidelis,' where 'in-' meant 'not' and 'fidelis' meant 'faithful.'

'infidelis' transformed into the Old French word 'infidèle,' and eventually became the modern English word 'infidel' through Middle English.

Initially, it meant 'unfaithful or disloyal,' but over time it evolved into its current meaning of 'a person who does not believe in a particular religion.'