'pro-annexation' originates from Latin and English components: the prefix 'pro-' (from Latin 'pro') meaning 'for' or 'in favor of', combined with 'annexation' (from Latin/Old French origins).

'annexation' comes from Latin elements (related to 'annexus', past participle of 'annectere'/'adnectere', from ad- 'to/toward' + nectere 'to bind'), passed into Old French as 'anexion'/'annexion' and then into Middle English as 'annexacioun' before becoming modern English 'annexation'. The modern compound 'pro-annexation' formed by adding the Latin-derived prefix 'pro-' to the established noun 'annexation' to indicate support.

Initially, roots related to 'annex' carried the idea of 'binding to' or 'joining to'. Over time, the combined term 'pro-annexation' has come to mean specifically 'in favor of incorporating territory or jurisdiction into another state', a political stance rather than a literal binding.