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 of hazardous

• 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 17 Americans aboard the MV Hondius are expected to be flown to the United States and monitored at the National Quarantine Unit at the University of Nebraska Medical Center, a specialized facility for highly hazardous communicable diseases. —Kayla Hayempour, NBC news, 10 May 2026

The search operation that involved more than 100 personnel supported by drones resumed early Saturday, focusing on a 700 square-meter (7,500 square-foot) area where clues were found during earlier searches, despite hazardous terrain and continuing eruptions, according to Ramdani. —ABC News, 9 May 2026

Rescue teams face hazardous conditions and continuing eruptions as Indonesia maintains an elevated alert for the volcano. —Los Angeles Times, 9 May 2026

Project work can include removal and disposal of hazardous and regulated materials; demolition; removal, transport and disposal of associated debris; backfilling; grading and site restoration; traffic maintenance; and soil erosion and sedimentation control. —Maya Wilkins, Chicago Tribune, 8 May 2026

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