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xeno- Prefix "foreigner"

Very early 20th cent. Borrowed from Ancient Greek ξένος ‎(ksénos) "foreign." Mycenaean ke-se-nu-wo (ksenwos). Of unknown origin, possibly borrowed from a non-Indo-European language.

"The free man, born into a group, is opposed to the stranger (Gr. xénos), that is to say, the enemy (Lat. hostis), who is liable to become my guest (Gr. xénos, Lat. hospes) or my slave if I capture him in war (Gr. aikhmálōtos, Lat. captivus)." ~ E. Benveniste, Indo-European Language and Society (1973)