1899 as shortened form of automobile (q.v.). Similar evolution yielded French, German auto.
also autoerotic, 1898, coined by Havelock Ellis from auto- + erotic. Related: Auto-eroticism (1898). The opposite is allo-erotic.
By "auto-erotism" I mean the phenomena of spontaneous sexual emotion generated in the absence of an external stimulus proceeding, directly or indirectly, from another person. [Ellis, "Auto-Erotism," in The Alienist and Neurologist, April 1898]
also auto-suggestion, "hypnotic or subconscious adoption of an idea by one's own effort," 1879, a hybrid from auto- + suggestion. The idea, and probably the model for the word, are from French.
word-forming element meaning "self, one's own, by oneself, of oneself" (and especially, from 1895, "automobile"), from Greek autos, reflexive pronoun, "self, same," which is of unknown origin. It also was a common word-forming element in ancient Greek, as in modern English, but very few of the old words have survived the interval. In Greek, as a word-forming element, auto- had the sense of "self, one's own, of oneself ('independently'); of itself ('natural, native, not made'); just exactly; together with." Before a vowel, it became aut-; before an aspirate, auth-. In Greek it also was used as a prefix to proper names, as in automelinna "Melinna herself." The opposite prefix would be allo-.