coarse (adj.)

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.