'pro-foreign' is formed from the Latin prefix 'pro-' meaning 'for' combined with the English word 'foreign', which ultimately comes from Old French 'forain' and Latin 'foraneus' meaning 'outside' or 'from outside'.

The element 'foreign' changed from Old French 'forain' and Middle English forms (e.g. 'foren', 'forain') into modern English 'foreign'. The prefix 'pro-' derives directly from Latin 'pro' and has been used in English as a productive prefix meaning 'in favor of' or 'for'. These elements combined in modern usage to form compounds like 'pro-foreign'.

Originally the parts signified 'for' + 'outside/other'; over time the compound came to mean 'in favor of foreign people, influence, or relations' rather than a literal spatial sense of 'for the outside'.