'anti-annexation' is formed from the Greek-derived prefix 'anti-' meaning 'against' combined with 'annexation,' from Latin origins; 'annexation' comes via Medieval Latin 'annexatio' from Latin elements 'ad-' (to) + 'nectere' (to bind).

'anti-' (from Greek anti- meaning 'against') was attached to the noun 'annexation' (from Medieval Latin 'annexatio' and Latin 'annectere') in modern English political usage, producing the compound 'anti-annexation' used in 19th–20th century and later discourse to denote opposition to territorial incorporation.

The parts retained their original senses: 'anti-' initially meant 'against' and 'annexation' initially meant 'the act of joining or attaching (territory)'; together they have consistently meant 'opposition to annexing/attaching territory' in modern usage.