'non-believer' originates from the prefix 'non-' meaning 'not' and the word 'believer,' which comes from Old English 'belȳfan,' meaning 'to have faith or trust.'

'belȳfan' transformed into the Middle English word 'bileven,' and eventually became the modern English word 'believe,' with 'non-believer' forming as a compound word.

Initially, it meant 'one who does not believe,' and this meaning has largely remained the same in modern usage.