Denim is 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.
The History of Denims
A popular conception of the etymology of the word denim is that it is a contraction or derivative of the French term, serge de Nîmes. 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), from which the first denim trousers were made.
A similarly woven traditional American cotton textile is the diagonal warp-striped hickory cloth that was once associated with railroad mens overalls, in which blue or black contrasting with undyed white threads form the woven pattern. Hickory cloth was characterized as being as rugged as hickory wood-not to mention the fact that it was deemed to be worn mainly by "hicks"-although neither may be the origin of that term [from a nickname for "Richard"]. Records of a group of New Yorkers headed for the California gold fields in 1849 show that they took along four "hickory shirts" apiece. Hickory cloth would later furnish the material for some "fatigue" pantaloons and shirts in the American Civil War.