c. 1300, ferren, foran, foreyne, in reference to places, "outside the boundaries of a country;" of persons, "born in another country," from Old French forain "strange, foreign; outer, external, outdoor; remote, out-of-the-way" (12c.), from Medieval Latin foraneus "on the outside, exterior," from Latin foris (adv.) "outside," literally "out of doors," related to foris "a door" (from PIE *dhwor-ans-, suffixed form of root *dhwer- "door, doorway").
English spelling altered 17c., perhaps by influence of reign, sovereign. Sense of "alien to one's nature, not connected with, extraneous" attested late 14c. Meaning "pertaining to another country" (as in foreign policy) is from 1610s. Replaced native fremd. Related: Foreignness. Old English had ælþeodig, ælþeodisc "foreign," a compound of æl- "foreign" + þeod "people."