1. Historically, someone who is not a Greek; then it became a person living outside the boundary of the Roman empire and its civilization; applied especially to the northern nations that overthrew them; followed by anyone who existed outside the realm of Christian civilization.
2. A rude, savage, alien, wild, uncivilized person.
3. An uncultured person, or someone who has no sympathy with literary culture.
4. Applied by nations, generally depreciatively, to foreigners; thus at various times and with various speakers or writers: non-Hellenic, non-Roman (most usual), non-Christian.
5. Uncultivated, uncultured, crude, unsophisticated, uncouth: "The artist accused the public of having barbarian tastes."
6. A foreigner, one whose language and customs differ from the speaker's.

From Greek barbaros, "non-Greek, foreign, barbarous," from an Indo-European imitative base barb, "to stammer, stutter; and unintelligible." The Greeks were quoted as saying that foreigners sounded as if they were saying, "Barbar, Barbar," which was, for the Greeks, unintelligible.