Emily Dickinson Lexicon

AU-THEN'TIC, or AU-THEN'TIC-AL, a. [Fr. authentique; It. and Sp. autentico; Low L. authenticus; from the Gr. αυθεντικος, from αυθεντης, an author or maker; one who does any thing by his own right; also one who kills himself. The first syllable is from αυτος, which is probably from the root of author, auctor; and the sense of self-murderer seems to indicate that the other constituent of the word is from θενω, θεινω, to kill, but the primary sense of which is, to strike, to drive or thrust with the hand, &c. In the word before us, the sense is to throw, or to set; hence authentic is set, fixed, made or made certain by the author, by one's own self.]

1. Having a genuine original or authority, in opposition to that which is false, fictitious, or counterfeit; being what it purports to be; genuine; true; applied to things; as an authentic paper or register.
2. Of approved authority; as an authentic writer.