internationalist noun 3adjective 1forms 3 noun3 •An advocate of internationalism. •A proponent of proletarian internationalism.A thorough-going internationalist, Marshall was a leading Boston organizer for the Peoples Anti-War Mobilization march of 100,000 at the Pentagon in 1981. — 1988 •A player representing their country in a team sport. adjective1 •Of or pertaining to internationalism.The apparatus is essentially ideological and internationalist in character and could not be replaced by the police, the army, or any other institution. — 1978 formsinternationalists · more internationalist · most internationalist