stranger n.

late 13c., straunge, "from elsewhere, foreign, unknown, unfamiliar, not belonging to the place where found," from Old French estrange "foreign, alien, unusual, unfamiliar, curious; distant; inhospitable; estranged, separated" (Anglo-French estraunge, strange, straunge; Modern French étrange), from Latin extraneus "foreign, external, from without" (source also of Italian strano "strange, foreign," Spanish extraño), from extra "outside of" (see extra-). In early use also strounge. The surname Lestrange is attested from late 12c. Sense of "queer, surprising" is attested from c. 1300, also "aloof, reserved, distant; estranged." In nuclear physics, from 1956.

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).