Denim as used for blue jeans, with a copper rivet to strengthen the pocket. Denim, in American usage since the late eighteenth century, denotes a rugged cotton twill textile, in which the weft passes under two (twi- "double") or more warp fibers, producing the familiar diagonal ribbing identifiable on the reverse of the fabric, which distinguishes denim from cotton duck. The word comes from the name of a sturdy fabric called serge, originally made in Nimes, France, by the Andre family. Originally called serge de Nimes, the name was soon shortened to denim. Denim was traditionally colored blue with indigo dye to make blue "jeans," though "jean" then denoted a different, lighter cotton textile; the contemporary use of jean comes from the French word for Genoa, Italy (Gênes), where the first denim trousers were made.
Aux origines du Denim: