foreigner (n.)

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."

English agent noun ending, corresponding to Latin -or. In native words it represents Old English -ere (Old Northumbrian also -are) "man who has to do with," from Proto-Germanic *-ari (cognates: German -er, Swedish -are, Danish -ere), from Proto-Germanic *-arjoz. Some believe this root is identical with, and perhaps a borrowing of, Latin -arius (see -ary).

Generally used with native Germanic words. In words of Latin origin, verbs derived from past participle stems of Latin ones (including most verbs in -ate) usually take the Latin ending -or, as do Latin verbs that passed through French (such as governor); but there are many exceptions (eraser, laborer, promoter, deserter; sailor, bachelor), some of which were conformed from Latin to English in late Middle English.

The use of -or and -ee in legal language (such as lessor/lessee) to distinguish actors and recipients of action has given the -or ending a tinge of professionalism, and this makes it useful in doubling words that have a professional and a non-professional sense (such as advisor/adviser, conductor/conducter, incubator/incubater, elevator/elevater).