Why is the ninth month called September?
1660s, a term in painting and sculpture, from French contour "circumference, outline," from Italian and Medieval Latin contornare "to go around," from Latin com-, intensive prefix (see com-), + tornare "to turn (on a lathe);" see turn (v.).
First recorded application to topography is from 1769. Earlier the word was used to mean "bedspread, quilt" (early 15c.) in reference to its falling over the sides of the mattress. Related: Contoured. Contour line in geography is from 1844.