Dialect levelling (or leveling in American English) is an overall reduction in the variation or diversity of features, accompanied by an increase in the similarities, between two or more dialects in contact with each other.[1] This can come about through assimilation, mixture, and merging of certain dialects, often by language codification, which can be a precursor to standardization. One possible result is a koine language, in which various specific dialects mix together and simplify, settling into a new and more widely embraced form of the language. Another is a speech community increasingly adopting or exclusively preserving features with widespread social currency at the expense of their more local or traditional dialect features.[2]
Dialect levelling has been observed in most languages with large numbers of speakers after industrialization and modernization of the areas in which they are spoken. However, while less common, it could be observed in pre-industrial times too, especially in colonial dialects like American and Australian English or when sustained linguistic contact between different dialects over a large geographical area continues for long enough as in the Hellenistic world that produced Koine Greek as a result of dialect leveling from Ancient Greek dialects.