Rosetta Stone

Proper noun

the Rosetta Stone

1. A large inscribed stone found near Rosetta, Egypt, in 1799, later used as a basis for understanding many previously undecipherable examples of hieroglyphic writing.
2. (broadly) Any source of information crucial to interpreting.
   • My friend’s carefully-compiled notebook was the Rosetta Stone that opened up understanding of the physics lectures.
   • Deputy team leader Larry Soderblom and team member Carl Sagan argued that the surfaces of these satellites, in their cratering history, would be a Rosetta stone for understanding the early years of the outer solar system.1990 August, Bradford A. Smith, “Voyage of the Century”, in National Geographic, volume 178, number 2, page 53