run-of-the-mill

The phrase originates from early 20th-century American manufacturing, specifically the milling of finished goods like lumber, cloth, or metal. The term "run of the mill" referred to the standard, ungraded output of a mill as it was produced, before any sorting for quality. This literal meaning of "the ordinary product from a mill's standard operation" was first recorded around 1930. By the 1940s, it had been lexicalized into the hyphenated adjective "run-of-the-mill," extending the industrial metaphor to describe anything commonplace, average, or lacking special distinction. Its evolution perfectly illustrates how a technical term from industry can transition into general language to convey the concept of standard, unexceptional quality.

This is a fixed compound adjective derived from an industrial idiom. It is not productively formed from separable modern morphemes.