From Longman Dictionary of Contemporary Englishboiler suitˈboiler suit noun [countable] British EnglishDCC a piece of loose clothing like trousers and a shirt joined together, that you wear over your clothes to protect them → overalls
Examples from the Corpus
boiler suit• New husband Guy Ritchie looked on wearing a blue boiler suit and trainers.• One wears a blue boiler suit with a white logo.• Overalls: Full bodied boiler suit style overalls are sufficient protection for most activities.• It may have been the way the exhaust pipe stained his boiler suit.• Beneath the boiler suit Morpurgo wore a shirt and tie. 