noxious

adjective

nox·​ious ˈnäk-shəs 

1

a

: physically harmful or destructive to living beings

noxious waste

noxious fumes

b

: constituting a harmful influence on mind or behavior

especially : morally corrupting

noxious doctrines

2

: disagreeable, obnoxious

… this noxious political scandal.

—H. L. Ickes

noxiously adverb

noxiousness noun

Synonyms of noxious

• poisonous
• toxic
• unhealthful
• unwholesome

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

Jennings was charged with two counts of first-degree assault, possession of a noxious matter and weapons possession and pleaded not guilty Tuesday at his arraignment. —Joseph Wilkinson, New York Daily News, 10 Feb. 2026

He is being charged with two counts of assault and possession of noxious material. —Alexa Herrera, CBS News, 10 Feb. 2026

What used to look like freedom now looks like a noxious lack of boundaries. —Nate Jones, Vulture, 31 Jan. 2026

The canister flooded the family’s vehicle with noxious gas. —Hannah Fingerhut, Los Angeles Times, 17 Jan. 2026

Word History

Etymology

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

Rhymes for noxious

• obnoxious

Kids Definition

noxious

adjective

nox·​ious ˈnäk-shəs 

: harmful especially to health : unwholesome

noxious fumes

Medical Definition

noxious

adjective

nox·​ious ˈnäk-shəs 

: physically harmful or destructive to living beings

noxious wastes