nox·​ious ˈnäk-shəs How to pronounce noxious (audio)
: physically harmful or destructive to living beings
noxious waste
noxious fumes
: constituting a harmful influence on mind or behavior
especially : morally corrupting
noxious doctrines
: disagreeable, obnoxious
this noxious political scandalH. L. Ickes
noxiously adverb
noxiousness noun
Choose the Right Synonym for noxious

pernicious, baneful, noxious, deleterious, detrimental mean exceedingly harmful.

pernicious implies irreparable harm done through evil or insidious corrupting or undermining.

the claim that pornography has a pernicious effect on society

baneful implies injury through poisoning or destroying.

the baneful notion that discipline destroys creativity

noxious applies to what is both offensive and injurious to the health of a body or mind.

noxious chemical fumes

deleterious applies to what has an often unsuspected harmful effect.

a diet found to have deleterious effects

detrimental implies obvious harmfulness to something specified.

the detrimental effects of excessive drinking

Examples of noxious in a Sentence

mixing bleach and ammonia can cause noxious fumes that can seriously harm you noxious smog that for years has been encrusting the historic cathedral with soot
Recent Examples on the Web Every year in the late fall, as air pollution in the Indian capital climbs to noxious extremes, the government takes emergency measures like closing schools, restricting traffic and banning construction. Sameer Yasir, New York Times, 12 Nov. 2023 The smoke came from the Canadian wildfires, mixed with the intense heat and humidity to create particularly noxious air for Midwesterners to breathe. Win McCormack, The New Republic, 14 Sep. 2023 The smog, a dangerous cocktail of particulate matter and noxious gasses, results from a series of unfortunate events that happen at the start of winter. WIRED, 13 Nov. 2023 For years, Gab has courted some of the most noxious personalities on the far right to participate on its platform, from Catholic antisemite E. Michael Jones to white supremacist groyper king Nick Fuentes. Kathryn Joyce, The New Republic, 12 Sep. 2023 In Greece, Italy, Canada and Algeria, raging wildfires ignited amid broiling temperatures, spewing noxious smoke and sending residents and tourists fleeing for safety. Hayley Smith Los Angeles Times (tns), al, 15 Aug. 2023 For example, myrtle spurge, a succulent that sprouts yellow and white flowers, is an invasive species that the Salt Lake County Health Department considers a noxious weed. Paige Ney, The Salt Lake Tribune, 26 Aug. 2023 Advertisement Just how noxious are the sewer gases passing through the neighborhoods near the polluted Tijuana River? Tammy Murga, San Diego Union-Tribune, 8 Oct. 2023 For years, Luna and his neighbors have withstood noxious odors and poisonous chemicals percolating from wells beneath their feet. Tony Briscoe, Los Angeles Times, 3 Oct. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'noxious.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Middle English noxius, borrowed from Latin noxius "guilty, delinquent, harmful, injurious" (derivative of noxa "injurious behavior, harm, mischief") + -us -ous; noxa derivative (perhaps with -s- as a desiderative suffix) from the base of nocēre "to damage (things), injure, harm (persons)," going back to Indo-European *noḱ-éi̯e- "destroy" (with semantic weakening in Latin), whence also Sanskrit nāśáyati "(s/he) destroys," causative derivatives from a verbal base *neḱ- "disappear, pass out of existence, perish," whence, with varying ablaut grades, Sanskrit náśyati "(s/he) is lost, perishes," Avestan nąsat̰ "has gone away, is lost," Tocharian B näk- "destroy," (in middle voice) "disappear, be destroyed"

Note: The Indo-European verbal base *neḱ- is also the source of a root noun attested as Latin nec-, nex "violent death, killing"; see necro-.

First Known Use

15th century, in the meaning defined at sense 1a

Time Traveler
The first known use of noxious was in the 15th century

Dictionary Entries Near noxious

Cite this Entry

“Noxious.” Dictionary, Merriam-Webster, Accessed 2 Dec. 2023.

Kids Definition


nox·​ious ˈnäk-shəs How to pronounce noxious (audio)
: harmful especially to health : unwholesome
noxious fumes

Medical Definition


nox·​ious ˈnäk-shəs How to pronounce noxious (audio)
: physically harmful or destructive to living beings
noxious wastes

More from Merriam-Webster on noxious

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