Koine

1. A dialect of Greek that developed primarily from Attic and became the common language of the Hellenistic world, from which later stages of Greek are descended.
2. koine A lingua franca.
3. koine A regional dialect or language that becomes the standard language over a wider area, losing its most extreme local features.

[From Greek (hē) koinē (dialektos), common (language), feminine of koinos, common.]

The noun has one meaning:

Meaning #1: a Greek dialect that flourished under the Roman Empire