Today, most people call the northern Italian port city where Christopher Columbus was born, Genoa, but it used to be known as Gênes, (the French word for Genoa).

In the 15th century, Italian workers in Genoa used a heavyweight fabric, similar to corduroy, for workwear. Usually made into trousers, the cloth was popular with sailors and fishermen. Since the fabric was made in Genoa, it was known as ‘Jean’ or ‘Gêne’. By the 17th century, jean was commonly worn by the working class in Northern Italy.

Meanwhile, In Nîmes, France, weavers (trying to reproduce jean fabric) had created a twill fabric that became known as ‘de Nîmes’ (from Nîmes). The new fabric, ‘denim’, was coarser, more durable, and better suited for aprons and overalls.

By the 19th century, versions of both fabrics were available in America, being used in totally different kinds of work clothes: jean in outfits for office workers; tougher denim for manual laborers. A Nevada tailor named Jacob Davis (1931-1908) noticed work pants always seemed to rip at the pockets. He began using rivets to reinforce stress points; an idea he patented in 1873, with help from his fabric supplier, Levi Strauss. Davis and Strauss experimented with different fabrics; finding denim to be more suitable, they began using it.

Jean, the other workwear fabric, faded in popularity, but the word didn’t; people continued to call their work pants, jeans.

That’s how an American invention, made with French fabric, got an Italian name.

More Info: en.wikipedia.org