Ancient tablet, pink and dry, son ate stupidly (7,5)
I believe the answer is:
rosetta stone
'ancient tablet' is the definition.
(I know that Rosetta Stone is ancient)
'pink and dry son ate stupidly' is the wordplay.
'pink' becomes 'rose' (colour).
'and' says to put letters next to each other.
'dry' becomes 'tt' (abbreviation for teetotal).
'stupidly' is an anagram indicator (a stupid ordering of the letters).
'son'+'ate'='sonate'
'sonate' anagrammed gives 'astone'.
'rose'+'tt'+'astone'='ROSETTA STONE'
(Other definitions for rosetta stone that I've seen before include "Tablet that was the key to deciphering Egyptian hieroglyphs" , "Inscribed basalt slab (found 1799), key to deciphering Egyptian hieroglyphs" , "Inscribed slab found 1799, making it possible to decipher Egyptian hieroglyphics" , "this revealed the tongue" , "This explained baffling script" .)