Rosetta stone has 2 different meanings across 2 categories:
a part of an inscribed granite stela that was originally about six feet tall and was set up in 196 BC; the inscriptions in hieroglyphics and Demotic and Greek gave the first clues to the decipherment of Egyptian hieroglyphics
A large inscribed stone found near Rosetta, Egypt, in 1799, later used as a basis for understanding many previously undecipherable examples of hieroglyphic writing.