| Definition -
The dialect of a region's common people; as opposed to the dialect of the upper classes.
1. According to the OED, "French scholars distinguish dialects as the particular forms presented by a language in different regions, so long as there does not exist a common written language. When a common language has become established as the medium of general literature, the dialects lose their literary standing and become patois."
Etymology - The word means "rough speech" in French, and it perhaps derives from the Old French patoier, treat roughly.
Oxford English Dictionary - Its first citation in this sense is from 1643:
"The Jargon and Patois of several Provinces."
(Sir T. Browne Relig. Med. ii. §8)