'annex' originates from Latin, specifically the past participle 'annexus' (from the verb 'annectere'), where the prefix 'ad-' meant 'to/toward' and the root 'nectere' meant 'to bind.'

'annex' passed into Anglo-French/Middle French as 'annexer' and Middle English as 'annexen', and eventually became the modern English word 'annex'.

Initially it meant 'to bind or tie to' (literally to join by binding), and over time it evolved into the modern sense of 'to attach or incorporate (often territory)'.