koine(n = noun.communication) interlanguage, lingua franca - a common language used by speakers of different languages; "Koine is a dialect of ancient Greek that was the lingua franca of the empire of Alexander the Great and was widely spoken throughout the eastern Mediterranean area in Roman times"
koine, n.
1 the common language of the Greeks from the close of the classical period to the Byzantine era.
2 a common language shared by various peoples; a lingua franca.