A loose protective coverall or smock worn over ordinary clothing for dirty work WordNet 3.0 & Open English WordNet

A boilersuit, also known as coveralls, is a loose fitting garment covering the whole body except for the head, hands and feet. Wikipedia

A garment also known as an overall or overalls Wikipedia Disambiguation

A garment worn over other clothing to protect it; a coverall or boiler suit. A garment, for manual labor or for casual wear, often made of a single piece of fabric, with long legs and a bib upper, supported from the shoulders with straps, and having several large pockets and loops for carrying tools. Wiktionary