a. [ OE. autentik, OF. autentique, F. authentique, L. authenticus coming from the real author, of original or firsthand authority, from Gr. &unr_;, fr. &unr_; suicide, a perpetrator or real author of any act, an absolute master; a'yto`s self + a form "enths (not found), akin to L. sons and perh. orig. from the p. pr. of e'i^nai to be, root as, and meaning the one it really is. See Am, Sin, n., and cf. Effendi.] 1. Having a genuine original or authority, in opposition to that which is false, fictitious, counterfeit, or apocryphal; being what it purports to be; genuine; not of doubtful origin; real; as, an authentic paper or register. [1913 Webster]

To be avenged
On him who had stole Jove's authentic fire. Milton. [1913 Webster]

2. Authoritative. [Obs.] Milton. [1913 Webster]

3. Of approved authority; true; trustworthy; credible; as, an authentic writer; an authentic portrait; authentic information. [1913 Webster]

4. (Law) Vested with all due formalities, and legally attested. [1913 Webster]

5. (Mus.) Having as immediate relation to the tonic, in distinction from plagal, which has a correspondent relation to the dominant in the octave below the tonic. [1913 Webster]

Syn. -- Authentic, Genuine. These words, as here compared, have reference to historical documents. We call a document genuine when it can be traced back ultimately to the author or authors from whom it professes to emanate. Hence, the word has the meaning, “not changed from the original, uncorrupted, unadulterated:” as, a genuine text. We call a document authentic when, on the ground of its being thus traced back, it may be relied on as true and authoritative (from the primary sense of “having an author, vouched for”); hence its extended signification, in general literature, of trustworthy, as resting on unquestionable authority or evidence; as, an authentic history; an authentic report of facts. [1913 Webster]

A genuine book is that which was written by the person whose name it bears, as the author of it. An authentic book is that which relates matters of fact as they really happened. A book may be genuine without being, authentic, and a book may be authentic without being genuine. Bp. Watson. [1913 Webster]

It may be said, however, that some writers use authentic (as, an authentic document) in the sense of “produced by its professed author, not counterfeit.” [1913 Webster]

n. An original (book or document). [ Obs. ] “Authentics and transcripts.” Fuller. [ 1913 Webster ]

a. Authentic. [ Archaic ] [ 1913 Webster ]

adv. In an authentic manner; with the requisite or genuine authority. [ 1913 Webster ]

n. The quality of being authentic; authenticity. [ R. ] Barrow. [ 1913 Webster ]

v. t. [ imp. & p. p. Authenticated p. pr. & vb. n. Authenticating (&unr_;). ] [ Cf. LL. authenticare. ] 1. To render authentic; to give authority to, by the proof, attestation, or formalities required by law, or sufficient to entitle to credit. [ 1913 Webster ]

The king serves only as a notary to authenticate the choice of judges. Burke. [ 1913 Webster ]

2. To prove authentic; to determine as real and true; as, to authenticate a portrait. Walpole. [ 1913 Webster ]

adj. 1. established or certified as genuine.
Syn. -- attested, documented. [ WordNet 1.5 ]

n. a mark on an article of trade to indicate its origin and authenticity.
Syn. -- hallmark, assay-mark. [ WordNet 1.5 ]

2. validating the authenticity of something or someone.
Syn. -- certification. [ WordNet 1.5 ]

n. [ Cf. F. authenticité. ] 1. The quality of being authentic or of established authority for truth and correctness. [ 1913 Webster ]

2. Genuineness; the quality of being genuine or not corrupted from the original. [ 1913 Webster ]

☞ In later writers, especially those on the evidences of Christianity, authenticity is often restricted in its use to the first of the above meanings, and distinguished from qenuineness. [ 1913 Webster ]

adv. Authentically. [ 1913 Webster ]