'aftmost' originates from Old English, specifically the word 'æftemest,' where 'æft' meant 'after' or 'behind' and '-mest' was a superlative suffix.

'æftemest' transformed into the Middle English word 'aftemest,' and eventually became the modern English word 'aftmost'.

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