Authentic

authentic , authoritative , genuine : Often misused as synonymous terms. That which accords with the facts and comes from the source alleged is authentic ; that which has the character represented and is true to its own claims is genuine ; that which possesses or emanates from proper authority and is entitled to acceptance as such is authoritative.

Trench in “On the Study of Words” (p. 189), says: “A genuine work is one written by the author whose name it bears; an authentic work is one which relates truthfully the matters of which it treats.” And an authoritative work is one which contains the results of the observations and conclusions of an author of special ability in subjects of which he is an acknowledged master.