rōˈze]d.ə-, ]tə- noun
Usage: usually capitalized R
Etymology: Rosetta stone, stone found in 1799 that is celebrated for having furnished the first clue to the decipherment of Egyptian hieroglyphics since it bears an inscription in hieroglyphics, demotic characters, and Greek, from Rosetta, city in northern Egypt near which it was found
: something that furnishes the first clue to the decipherment of a previously incomprehensible system of ideas or state of affairs
the book can be its own Rosetta stone and it is an interesting game to try to ferret out meanings by comparing passages till the puzzle is solved — Ellsworth Faris