noxious

American  

[nok-shuhs] / ˈnɒk ʃəs /

adjective

1. harmful or injurious to health or physical well-being.

   noxious fumes.

   Synonyms:

   deleterious, detrimental, nocuous, unhealthy, unwholesome, hurtful

   Antonyms:

   harmless

2. morally harmful; corrupting; pernicious.

   a noxious plan to spread dissension.

   Synonyms:

   corruptive

   Antonyms:

   harmless

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noxious British  

/ ˈnɒkʃəs /

adjective

1. poisonous or harmful

2. harmful to the mind or morals; corrupting

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Other Word Forms

• noxiously adverb
• noxiousness noun

Etymology

Origin of noxious

1605–15; < Latin noxius harmful, hurtful, injurious, equivalent to nox ( a ) harm, hurt, injury (akin to nocēre to do harm, inflict injury; see innocent) + -ius -ious

Explanation

Something noxious is harmful and could be even fatal — whether it is colorless, odorless, and invisible like carbon monoxide, or dark, strong-smelling, and obvious, like black smoke from a fire. People are called noxious too when they hurt others with cruelty or mental anguish. English and Latin roots for noxious are related to the meanings of "harm," "damage," and "injury." While obnoxious might come to mind when seeing the word noxious, obnoxious is a much less damaging adjective to describe someone annoying. Most uses for noxious involve real physical or emotional damage unless the word is used in exaggeration. Examples range from "the noxious gas fumes made the dog pass out" to "his cologne was so noxious I had to exit the elevator and take the stairs."

Example Sentences

Like Kennedy, he failed to end a noxious regime, but he still has cards if he’s willing to play them.

From The Wall Street Journal • May 1, 2026

"So, they can cope with higher levels of noxious irritants produced by cold exposure."

From Science Daily • Mar. 26, 2026

The "Black Summer" bushfires raged across Australia's eastern seaboard from late 2019 to early 2020, razing millions of hectares, destroying thousands of homes and blanketing cities in noxious smoke.

From Barron's • Jan. 8, 2026

Toilets crawling with rats, maggots and flies became so noxious that neighbors began defecating on the surrounding dirt roads.

From Salon • Dec. 16, 2025

Dead animals were routinely tossed into this soup, where everything decayed and sent up noxious bubbles to foul the air.

From "An American Plague: The True and Terrifying Story of the Yellow Fever Epidemic of 1793" by Jim Murphy

Related Words

• corrupting
• destructive
• fetid
• harmful
• pernicious
• poisonous
• putrid
• toxic
• unhealthy
• virulent