'attorn' originates from Old French, specifically the word 'atorner' (also spelled 'attorner' or 'atorner'), where the prefix 'a-' was used and the root 'torner' meant 'to turn'.

'attorn' changed from Old French 'atorner' and Anglo-Norman usage into Middle English forms such as 'attournen' and eventually became the modern English verb 'attorn' (with past/past-participle 'attorned').

Initially it meant 'to turn (one's allegiance or attention) to someone', but over time it evolved into the legal sense of 'to acknowledge a new lord/landlord or to transfer/submit one's tenancy or obligations,' which is its common modern usage.