Real Dictionary

overalls in American English
loose, sturdy trousers, usually with a bib or biblike piece to which shoulder straps are attached, originally worn over other trousers to protect them, as by factory workers or farmers
loosefitting trousers of some strong cotton cloth, often with a part extending up over the chest, worn, usually over other clothing, to protect against dirt and wear

overalls in British English
plural noun: hard-wearing work trousers with a bib and shoulder straps or jacket attached