Tablet enabling hieroglyphics to be deciphered (7,5)
I believe the answer is:
rosetta stone
(Other definitions for rosetta stone that I've seen before include "Inscribed slab found 1799, making it possible to decipher Egyptian hieroglyphics" , "this revealed the tongue" , "This explained baffling script" , "clue to civilisation" , "Champollion's key to Egyptian hieroglyphs" .)