'easternmost' originates from Old English, specifically the word 'ēasterne,' where 'ēast' meant 'east' and '-ern' was a suffix indicating direction, combined with 'most' to denote the furthest point.

'ēasterne' transformed into the Middle English word 'estern,' and eventually became the modern English word 'easternmost.'

Initially, it meant 'farthest to the east,' and this meaning has largely remained the same in modern usage.