Definition from Wiktionary, the free dictionary
From Ancient Greek κοινός (koine, “shared, common, public, general, ordinary, usual”)
Proper noun 
- The "common" Greek language that developed and flourished between 300 BCE and 300 CE (the time of the Roman Empire), and from which Modern Greek descended. It was based on the Attic and Ionian dialects of Ancient Greek.
common Greek language