koine

The “common” Greek language that developed and flourished between 300 B.C.E. and 300 C.E. (the time of the Roman Empire), and from which Modern Greek descended. It was based on the Attic and Ionian dialects of Ancient Greek.

A linguistic variety that has developed in supraregional contact between speakers of various interrelated dialects, typically in such a way that features shared by several dialects prevail and those of limited distribution are avoided.

A lingua franca.

If a dominant language was spoken in the area of such trade routes, then this dominant language became the ‘interlanguage’, as it is called. Such an interlanguage, or koiné, is a simplified dialect with which speakers of two or more quite different dialects communicate with one another.

Now, another term for that product is koine, which, however, I have regularly […] employed in reference to the infrastructure (procedural, juridical, formal, cultural) that enables and informs composition of a lingua franca. […] In linguistic scholarship koine mostly (!) refers to a standard language expanded by input from several dialectal sources with concomitant levelling of morphological and syntactic differences and adoption of a general and possibly restricted lexicon.