'annexationism' originates from English, specifically the word 'annexation' + the suffix '-ism', where 'annexation' ultimately comes from Latin 'annexare' meaning 'to attach' or 'to join.'

'annexation' changed from Latin 'annexatio' (via medieval/Old French forms such as 'anexacion') into Middle English 'annexacioun' and eventually modern English 'annexation'; 'annexationism' was formed in modern English by adding the suffix '-ism' to denote a doctrine or system.

Initially it referred to the act or process of attaching or adding ('to attach'), but over time it evolved into the current sense of 'the doctrine or policy of annexing territory.'