"native or inhabitant of ancient Media," the ancient kingdom south of the Caspian Sea, later a part of the Persian empire, late 14c., from Latin Medus, from Greek Medos "Mede," from the indigenous people-name Medes, which is said to be from the name of their first king (Medos).
c. 1300, Prestre Johan, legendary medieval Christian king and priest, said to have ruled either in the Far East or Ethiopia. Prestre (attested as a surname late 12c.) is from Vulgar Latin *prester, a transition between Latin presbyter and English priest. First mentioned in the West by mid-12c. chronicler Otto of Freising, who told how Johannes Presbyter won a great victory over the Persians and the Medes. Between 1165 and 1177 a forged letter purporting to be from him circulated in Europe. All this recalls the time when the Christian West was militarily threatened on its frontiers by Muslim powers, dreaming of a mythical deliverer. Compare Old French prestre Jehan (13c.), Italian prete Gianni.
early 15c., in reference to classical history, "a non-Roman or non-Greek," earlier barbar (late 14c.) "non-Roman or non-Greek person; non-Christian; person speaking a language different from one's own," from Medieval Latin barbarinus (source of Old French barbarin "Berber, pagan, Saracen, barbarian"), from Latin barbarus "strange, foreign, barbarous," from Greek barbaros "foreign, strange; ignorant," from PIE root *barbar- echoic of unintelligible speech of foreigners (compare Sanskrit barbara- "stammering," also "non-Aryan," Latin balbus "stammering," Czech blblati "to stammer").
Greek barbaroi (plural noun) meant "all that are not Greek," but especially the Medes and Persians; originally it was not entirely pejorative, but its sense became moreso after the Persian wars. The Romans (technically themselves barbaroi) took up the word and applied it to tribes or nations which had no Greek or Roman accomplishments.
Also in Middle English (c. 1400) "native of the Barbary coast;" meaning "rude, wild person" is from 1610s. Occasionally in 19c. English distinguished from savage (n.) as being a step closer to civilization. Sometimes, in reference to Renaissance Italy, "a non-Italian." It also was used to translate the usual Chinese word of contempt for foreigners.
Barbarian applies to whatever pertains to the life of an uncivilized people, without special reference to its moral aspects. Barbarous properly expresses the bad side of barbarian life and character, especially its inhumanity or cruelty: as, a barbarous act. Barbaric expresses the characteristic love of barbarians for adornment, magnificence, noise, etc., but it is not commonly applied to persons: it implies the lack of cultivated taste .... [Century Dictionary, 1889]