Word of the Day:

1 : a black basalt stone found in 1799 that bears an inscription in hieroglyphics, demotic characters, and Greek and is celebrated for having given the first clue to the decipherment of Egyptian hieroglyphics

2 : one that gives a clue to understanding

"This is the home of the Elliott wave principle, an arcane system of technical analysis that thousands of investors have come to believe is the Rosetta stone of the stock market." (Cynthia Crossen, The Wall Street Journal, March 18, 1987)

More example sentences

The word "hieroglyphics" refers to an Egyptian writing system that was unintelligible to later civilizations until an inscribed stone about the size of a coffee table was discovered over 200 years ago in an Egyptian town called Rosetta ("Rashid" in Arabic). The Rosetta stone, as it came to be called, held a key to the ancient writing system. Probably written by Egyptian priests in the 2nd century B.C., its hieroglyphic text repeated a text written in familiar Greek. As a result, Egyptologists were able to decipher the symbols. Today we also use "Rosetta stone" figuratively, as we have since the early 20th century, for other things that provide clues or help us to understand something that would otherwise be undecipherable.