'annexatory' originates from Latin, specifically the word 'annectere' (related to the past participle 'annexus'), where the prefix 'ad-' meant 'to' (assimilated as 'an-' before n) and 'nectere' meant 'to bind or tie'.

'annexatory' changed through Medieval and Late Latin forms (such as Medieval Latin 'annexare'/'annexus'), passed into Old French as 'annexer' and into Middle English as 'annex' with English adjective-forming suffixes (‑atory), eventually becoming the modern English adjective 'annexatory'.

Initially, the root meant 'to bind or attach,' but over time it evolved into meanings associated with 'attaching territory or incorporating by annexation,' which is reflected in the modern sense 'relating to annexation or tending to annex.'