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
- grave
- grievous
- jeopardizing
- menacing
- parlous
- perilous
- risky
- serious
- threatening
- unhealthy
- unsafe
- venturesome
See all Synonyms & Antonyms 
Example Sentences
It was a hazardous voyage. These are hazardous chemicals that can cause death if inhaled.
Recent Examples on the Web When exposed to smoke and pet hair, this device quickly reduced the room's PM 2.5 levels from 999 (hazardous) to 2.8 after just 10 minutes on its lowest setting. 
Samantha Jones, Better Homes & Gardens, 18 Sep. 2022 In parking lots, on flatbed trucks, hospital courtyards and rooftops, private generators are ubiquitous, spewing hazardous fumes into homes and businesses around the clock. Amy Hubbard, Los Angeles Times, 16 Sep. 2022 Long-distance Amtrak passenger services, which use freight tracks, and hazardous materials shipments are now being restored after railroads suspended them to prevent people or cargo becoming stranded by a strike. WIRED, 16 Sep. 2022 The Wall Street Journal is reporting Amtrak has already canceled some long-distance trains, while a few freight rail operators have already stopped accepting hazardous goods. William Thornton | Wthornton@al.com, al, 15 Sep. 2022 Amtrak has already canceled some long distance routes and companies have moved to suspend hazardous shipments in case they get stranded mid-route. Abc News, ABC News, 14 Sep. 2022 Passenger rail provider Amtrak has canceled some long-distance trains and some freight rail operators have already stopped accepting hazardous goods. Austen Hufford, WSJ, 14 Sep. 2022 The fire’s colossal smoke plume brought bad air quality to most of the Bay Area this past weekend and hazardous-level smoke pollution to Tahoe and neighboring regions in Sacramento. Gerry Díaz, San Francisco Chronicle, 13 Sep. 2022 Some freight carriers have begun limiting services, suspending hazardous material shipments, and parking trains in what appears to be preparations for a lockout. Jeff Stein And Lauren Kaori Gurley, BostonGlobe.com, 13 Sep. 2022 See More
Samantha Jones, Better Homes & Gardens, 18 Sep. 2022 In parking lots, on flatbed trucks, hospital courtyards and rooftops, private generators are ubiquitous, spewing hazardous fumes into homes and businesses around the clock. Amy Hubbard, Los Angeles Times, 16 Sep. 2022 Long-distance Amtrak passenger services, which use freight tracks, and hazardous materials shipments are now being restored after railroads suspended them to prevent people or cargo becoming stranded by a strike. WIRED, 16 Sep. 2022 The Wall Street Journal is reporting Amtrak has already canceled some long-distance trains, while a few freight rail operators have already stopped accepting hazardous goods. William Thornton | Wthornton@al.com, al, 15 Sep. 2022 Amtrak has already canceled some long distance routes and companies have moved to suspend hazardous shipments in case they get stranded mid-route. Abc News, ABC News, 14 Sep. 2022 Passenger rail provider Amtrak has canceled some long-distance trains and some freight rail operators have already stopped accepting hazardous goods. Austen Hufford, WSJ, 14 Sep. 2022 The fire’s colossal smoke plume brought bad air quality to most of the Bay Area this past weekend and hazardous-level smoke pollution to Tahoe and neighboring regions in Sacramento. Gerry Díaz, San Francisco Chronicle, 13 Sep. 2022 Some freight carriers have begun limiting services, suspending hazardous material shipments, and parking trains in what appears to be preparations for a lockout. Jeff Stein And Lauren Kaori Gurley, BostonGlobe.com, 13 Sep. 2022 See More Word History
Etymology
see hazard entry 1
First Known Use
1549, in the meaning defined at sense 1
Kids Definition
hazardous
adjective
haz·ard·ous ˈha-zər-dəs
: dangerous sense 1 hazardous chemicals
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
hazardous
adjective
as in dangerous
involving potential loss or injury a hazardous journey across the arctic ice Synonyms & Similar Words
Relevance
- dangerous
- perilous
- risky
- unsafe
- serious
- precarious
- treacherous
- threatening
- unhealthy
- menacing
- jeopardizing
- grave
- grievous
- random
- harmful
- fatal
- destructive
- detrimental
- venturesome
- parlous
- uncertain
- unpleasant
- adverse
- lethal
- deadly
- bad
- insecure
- injurious
- haphazard
- sickening
- fell
- dicey
- ultrahazardous
- deleterious
- chance
- noxious
- ugly
- distressing
- malignant
- pernicious
- murderous
- evil
- nasty
- wicked
- hurtful
- ill
- killer
- dire
- inimical
- mortal
- baneful
- fateful
- deathly
- pestilent
- baleful
Antonyms & Near Antonyms
- nonhazardous
- safe
- harmless
- innocuous
- beneficial
- innocent
- nonthreatening
- advantageous
- good
- unthreatening
- ultrasafe
Synonym Chooser
Some common synonyms of hazardous are dangerous, perilous, precarious, and risky. While all these words mean "bringing or involving the chance of loss or injury," hazardous implies great and continuous risk of harm or failure.
claims that smoking is hazardous to your health
In some situations, the words dangerous and hazardous are roughly equivalent. However, dangerous applies to something that may cause harm or loss unless dealt with carefully.
soldiers on a dangerous mission
Although the words perilous and hazardous have much in common, perilous strongly implies the immediacy of danger.
perilous mountain roads
While the synonyms precarious and hazardous are close in meaning, precarious suggests both insecurity and uncertainty.
earned a precarious living by gambling
While in some cases nearly identical to hazardous, risky often applies to a known and accepted danger.
shied away from risky investments