supersecret

adj

1. Extremely secret or secretive

   “The changes come a year after a Sundance film, “This Film Is Not Yet Rated,” excoriated the rating system as a supersecret star chamber.”

noun

1. A piece of highly secret information.

   “While this author has argued that most of those "supersecrets" fell into American hands, or, worse, that the most radical and exotic of these supersecrets remained in Nazi hands after the war, Agoston's book is signally important in that it was the first public recounting of the Kammler Group and the first disclosure that much more was going on inside of Nazi Germany besides the development of jet aircraft and rockets.”