Merriam-Webster's Word of the Day for October 13, 2008 is:

koine • \koy-NAY\  • noun
1 : the Greek language commonly spoken and written in eastern Mediterranean countries in the Hellenistic and Roman periods *2 : a dialect or language of a region that has become the common or standard language of a larger area

Example sentence:
Koines inevitably developed in the early British colonies as different dialects converged.

Did you know?
Koine, which means "common" or "shared" in Greek, was the language spoken in the eastern Mediterranean countries from the 4th century B.C. until the time of the Byzantine emperor Justinian (mid-6th century A.D.). In linguistics, the word "koine" is applied to a language developed from contact between dialects of the same language over a large region. Basically, a koine adopts those grammatical and lexical elements from the dialects of the region that are easily recognized by most area speakers and dispenses with those that are not.

*Indicates the sense illustrated in the example sentence.