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 Last week, the International Monetary Fund warned of the noxious combination of lower growth and higher debt. Patricia Cohen, New York Times, 2 Apr. 2024 The man, identified as 25-year-old George Vassiliou, was charged with assault, harassment, possession of a weapon, unlawful possession of noxious matter and criminal contempt for violating a protection order, the NYPD said. Eric Lagatta, USA TODAY, 27 Mar. 2024 Officers batter protesters with plastic shields, and noxious plumes rise from the street where tear-gas canisters have been deployed. David Peisner, Rolling Stone, 24 Mar. 2024 But this isn’t the first time Arizona officials have alerted the public to the noxious weed. Helena Wegner, Sacramento Bee, 29 Mar. 2024 Minnesota: The state designated Callery pear trees as a noxious weed and has begun a three-year production phase-out period; the trees cannot be sold in 2026, according to the state's agriculture department. Mike Snider, USA TODAY, 25 Mar. 2024 But the astronauts’ mishandling of switches during descent allowed a noxious gas to enter their chamber, affecting the lungs of all three crewmen and resulting in their brief hospitalization upon landing. Richard Goldstein, New York Times, 18 Mar. 2024 Smoke from the fires, particularly blazes that burned in Quebec, wafted as far south as Florida and blanketed several cities in the United States and southern Canada in a noxious cloud. Ian Austen, New York Times, 4 Mar. 2024 This fascinating behavior, where the stomach is inverted, is believed to serve as a mechanism for expelling noxious or indigestible items from the gastrointestinal tract. Melissa Cristina Márquez, Forbes, 2 Mar. 2024

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 24 Apr. 2024.

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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