authentic WHAT?

Au-then-tic = worthy of acceptance or belief as conforming to or based on fact; not false; being fully trustworthy. Among the current marketing craze about "authenticity", I would really like to know why is this word used as a noun, and not as adjective? If used as a noun, it is kinda self-referential, like "this is authentic", "authentic brand" or, "authentic communication". This last one is particularly troubling to me, since I thought it should be given that communication is authentic = honest, and that no one should really take pride in that (like, marketing agencies figured out only NOW that they may want to consider communicating honestly ... and only when really cornered). So in this context, I suppose that what "authentic" should really refer to is the question of "what" [is communicated in ad messages needs to correspond to real-life consumers' experience with products/services that are advertised], and not "how" [to communicate ad messages]. In short, it's a question of doing, not of communicating. And if this is true, then the word should be used as adjective, as in [doing something] authentically ... Anyway, even without this analysis, got to admit that "authenticity" sounds like crap to me. (it's filed in the same folder as "engagement", "authentic engagement", and "the original maverick" )