'either' originates from Old English, specifically the word 'ǣgther,' where 'ǣg-' meant 'each' and '-ther' meant 'of two.'

'ǣgther' transformed into the Middle English word 'either,' and eventually became the modern English word 'either.'

Initially, it meant 'each of two,' but over time it evolved into its current meaning of 'one or the other of two.'