'adjoin' originates from Latin, specifically the word 'adjungere,' where 'ad-' meant 'to' and 'jungere' meant 'to join.'

'adjungere' transformed into the Old French word 'ajoindre,' and eventually became the modern English word 'adjoin' through Middle English.

Initially, it meant 'to join or connect,' and this meaning has largely remained the same in modern usage.