'internationalist' originates from English, formed from 'international' + the suffix '-ist'. 'international' ultimately comes via French from Latin 'inter-' meaning 'between' and 'natio' meaning 'birth, nation', while '-ist' (from French/Latin) denotes an adherent or advocate.

'internationalist' changed from French word 'internationaliste' and from English usage of the proper name 'International' (for organizations such as the International Working Men's Association); the modern English 'internationalist' emerged in the mid 19th century to denote members or supporters of such movements and later broadened.

Initially it often meant 'a member or supporter of an "International" (a transnational organization, especially of workers)'; over time it evolved into the broader current meaning of 'a person who supports international cooperation or internationalism' and is used in many contexts.