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

Example Sentences

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 Put another way, why is art so effective at washing away the gritty, noxious reality of human ambition, despite the obvious fact that the pharaohs, kings and courtiers of the past were no more substantial than the posers and parvenues of today? Philip Kennicott, Washington Post, 30 Dec. 2022 These noxious cells, along with the idea that getting rid of them could mitigate chronic illnesses and the discomforts of aging, are getting serious attention. Amber Dance, Smithsonian Magazine, 29 Dec. 2022 Some of America’s most noxious invasive plants—floating heart, Asiatic bittersweet, Japanese meadowsweets, princess tree, porcelain berry—are the botanical pets of aristocrats, gone feral. Sonya Bennett-brandt, WIRED, 22 Dec. 2022 Raw materials can be hard to mine, are often found in countries with poor human rights records and require processing that leaves behind noxious waste. Kellen Browning, New York Times, 21 Dec. 2022 Raw materials can be hard to mine, are often found in countries with poor human rights records, and require processing that leaves behind noxious waste. Niraj Chokshi,, 21 Dec. 2022 The brain may trigger such sickening odors instead of agreeable ones because humans learned very early to avoid noxious smells for survival. NBC News, 21 Dec. 2022 Those who have tried to craft effective online moderation policies do so because noxious and vicious attacks and invective don’t encourage more open discussion, but drive thoughtful participants out of the discussion. Michael Hiltzik, Los Angeles Times, 14 Dec. 2022 And the state of New York can't prohibit noxious speech because of it as well. Bradley Gitz, Arkansas Online, 12 Dec. 2022 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'noxious.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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 Feb. 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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