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

'annex' changed from Latin 'annectere'/'annexus' to Medieval/Old French 'annexer' and entered Middle English as 'annex', eventually becoming the modern English 'annex'.

Initially, it meant 'to bind or attach', but over time it evolved into its current meaning of 'to add or incorporate (especially territory) to a larger entity'.