hazardous

adjective

haz·​ard·​ous ˈha-zər-dəs 

1

: involving or exposing one to risk (as of loss or harm)

a hazardous occupation

disposing of hazardous waste

2

: depending on the effect of unpredictable and unanalyzable forces in determining events : depending on hazard (see hazard entry 1 sense 2a) or chance

hazardous outcomes

hazardously adverb

hazardousness noun

Synonyms

• dangerous
• perilous
• risky
• serious
• unsafe

Choose the Right Synonym for hazardous

dangerous, hazardous, precarious, perilous, risky mean bringing or involving the chance of loss or injury.

dangerous applies to something that may cause harm or loss unless dealt with carefully.

soldiers on a dangerous mission

hazardous implies great and continuous risk of harm or failure.

claims that smoking is hazardous to your health

precarious suggests both insecurity and uncertainty.

earned a precarious living by gambling

perilous strongly implies the immediacy of danger.

perilous mountain roads

risky often applies to a known and accepted danger.

shied away from risky investments

Examples of hazardous in a Sentence

It was a hazardous voyage.

These are hazardous chemicals that can cause death if inhaled.

Recent Examples on the Web

The pace of the 2025 fires is reminiscent of the record-breaking 2023 wildfire season, which exposed millions of people in North America to hazardous smoke levels. —Jun Wang, Space.com, 9 Aug. 2025

The collapse of the bridge also caused hazardous debris to enter the Colorado River waterway. —Wren Smetana, AZCentral.com, 9 Aug. 2025

In addition, a hazmat crew responded on standby due to hazardous materials stored in the building but away from the fire area. —Darcie Moran, Freep.com, 7 Aug. 2025

With over 700 wildfires still active in Canada, conditions may remain hazardous in the coming days. —Hannah Parry amanda Castro, MSNBC Newsweek, 4 Aug. 2025

Word History

Etymology

see hazard entry 1

First Known Use

1549, in the meaning defined at sense 1

Rhymes for hazardous

• nonhazardous

Kids Definition

hazardous

adjective

haz·​ard·​ous ˈhaz-ərd-əs 

: dangerous sense 1, risky

hazardously adverb

hazardousness noun

Legal Definition

hazardous

adjective

haz·​ard·​ous

: creating a hazard : involving or exposing one to risk (as of loss or harm)

a hazardous occupation

a hazardous substance

hazardously adverb