Hazardous means full of danger to health or safety. Hazardous waste, hazardous conditions, hazardous to health.
It is the formal and regulatory word: hazardous substances, hazardous waste and hazardous area are all defined categories with rules attached. Dangerous is the everyday equivalent. In safety work, a hazard is anything that could cause harm and a risk is the chance of it doing so — the two are distinguished carefully and confused constantly. Note hazard, and hazard lights, which are the flashing ones on a car.
1adjectivehazardousFull of danger to health or safety.
“Workers must wear masks and gloves when handling hazardous chemicals.”
synonyms: dangerous, risky
hazardous is a quality of danger.
Also accepted in games: dangerous, risky
Old French hasard was a dice game, from an Arabic word for dice. A hazard was a game of chance before it was a danger, and the word gained its risk through gambling.
Middle French
hasardeux
English, today
hazardous
From Middle French hasardeux, equivalent to hazard + -ous.
Etymology from Wiktionary, CC BY-SA