'adjoin' originates from Old French, specifically the word 'ajoindre,' where 'a-' meant 'to' and 'joindre' meant 'join.'

'ajoindre' transformed into the Middle English word 'ajoinen,' and eventually became the modern English word 'adjoin.'

Initially, it meant 'to join or connect,' but over time it evolved into its current meaning of 'to be next to or in contact with.'