means A one-piece work garment combining trousers with a bib and shoulder straps that cover the front of the body, designed to protect clothing during heavy labor.

from A plain English compound, exactly what it says: the things you wear 'over all' your other clothes. The word predates the famous denim version by centuries, beginning as a term for protective outer garments before the 19th-century rise of rugged work clothing fixed it to the bib-and-strap trousers we picture today.