Words related to auto-
mid-14c., autentik, "authoritative, duly authorized" (a sense now obsolete), from Old French autentique "authentic; canonical" (13c., Modern French authentique) and directly from Medieval Latin authenticus, from Greek authentikos "original, genuine, principal," from authentes "one acting on one's own authority," from autos "self" (see auto-) + hentes "doer, being," from PIE root *sene- (2) "to accomplish, achieve." Sense of "real, entitled to acceptance as factual" is first recorded mid-14c.
Traditionally in modern use, authentic implies that the contents of the thing in question correspond to the facts and are not fictitious (hence "trustworthy, reliable"); while genuine implies that the reputed author is the real one and that we have it as it left the author's hand (hence "unadulterated"); but this is not always maintained: "The distinction which the 18th c. apologists attempted to establish between genuine and authentic ... does not agree well with the etymology of the latter word, and is not now recognized" [OED].
Which is it to be? We observe that the London Times has lent the weight of its authority to the word "autocar," which it now prints without the significant inverted commas but with a hyphen, "auto-car." We believe that the vocable originated with a journal called the Hardwareman, which succeeded in obtaining the powerful support of the Engineer for its offspring. As for ourselves, being linguistic purists, we do not care for hybrid constructions—"auto" is Greek, while "car" is Latin and Celtic. At the same time, such clumsy phrases as "horseless carriages," "mechanical road carriages," and "self-propelled vehicles" are not meeting with general favour. Why not therefore adopt the philogically sound "motor-car," which could be run into a single word, "motorcar"? [The Electrical Engineer, Dec. 20, 1895]
1640s, "one sprung from the soil he inhabits" (plural autochthones), from Latinized form of Greek autokhthon "aborigines, natives, primitive inhabitants," literally "sprung from the land itself," used of the Athenians and others who claimed descent from the Pelasgians, from autos "self" (see auto-) + khthōn "land, earth, soil" (from PIE root *dhghem- "earth").