'monotheist' originates from Greek, specifically the word 'monotheos,' where 'mono-' meant 'one' and 'theos' meant 'god.'

'monotheos' transformed into the French word 'monothéiste,' and eventually became the modern English word 'monotheist' through Middle English.

Initially, it meant 'believer in one god,' and this meaning has largely remained the same in modern usage.