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

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

The lagoon is the most biologically diverse estuary on the nation’s east coast, but the manatees, birds and fish that call it home are suffering dramatically from the death of seagrass and the abundance of noxious algae that thrive on polluted water. —Orlando Sentinel Editorial Board, The Orlando Sentinel, 11 Jan. 2026

Then she’s saddled with the noxious task of trying to convince Eleven (Millie Bobby Brown) to kill herself for the greater good, only to reverse course at the last second and save her? —Ben Travers, IndieWire, 1 Jan. 2026

One of the most noxious ideas, which is gaining traction among some MAGA devotees, is the concept of Christian nationalism. —Steven Greenhut, Oc Register, 5 Dec. 2025

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