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early 15c., cors "ordinary" (modern spelling is from late 16c.), probably adjectival use of noun cours (see course (n.)), originally referring to rough cloth for ordinary wear. Developed a sense of "rude" c.1500 and "obscene" by 1711. Perhaps related, via metathesis, to French gros, which had a similar sense development. Related: Coarsely; coarseness.