'adjoining' originates from Middle English, specifically the word 'ajoinen,' where 'a-' meant 'to' and 'joinen' meant 'join.'

'ajoinen' transformed into the modern English word 'adjoin,' and eventually became the adjective 'adjoining.'

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