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1766; as an adjective, "characteristic of the middle class" (depreciative) it dates from 1893.
A social and economic class composed of those more prosperous than the poor, or lower class, and less wealthy than the upper class. Middle class is sometimes loosely used to refer to the bourgeoisie. In the United States and other industrial countries, the term is often applied to white-collar, as opposed to blue-collar, workers.
Note: Values commonly associated with the middle class include a desire for social respectability and material wealth and an emphasis on the family and education.