deleterious

American  

[del-i-teer-ee-uhs] / ˌdɛl ɪˈtɪər i əs /

adjective

1. injurious to health.

   deleterious gases.

2. harmful; injurious.

   deleterious influences.

   Synonyms:

   noxious, destructive, hurtful, pernicious

   Antonyms:

   beneficial

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deleterious British  

/ ˌdɛlɪˈtɪərɪəs /

adjective

1. harmful; injurious; hurtful

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Other Word Forms

• deleteriously adverb
• deleteriousness noun
• nondeleterious adjective
• nondeleteriously adverb
• nondeleteriousness noun
• undeleterious adjective
• undeleteriously adverb
• undeleteriousness noun

Etymology

Origin of deleterious

1635–45; < Greek dēlētḗrios destructive, adj. derivative of dēlētḗr destroyer, equivalent to dēlē- variant stem of dēleîsthai to hurt, injure + -tēr agent suffix + -ios adj. suffix; -ious

Example Sentences

When they met in Munich last month, California Gov. Gavin Newsom sought his views on curbing the addictive and deleterious effects of social media on children.

From The Wall Street Journal • Mar. 27, 2026

"Those beneficial mutations in the old environment might become deleterious in the new environment."

From Science Daily • Dec. 24, 2025

But he demonstrated Wednesday that his leadership remains intact—and strong enough to prevent tension in the Fed’s dual mandate from devolving into deleterious tension within the committee.

From Barron's • Dec. 12, 2025

Directors, producers and owners of theater chains fear that Netflix’s WBD takeover can only be further deleterious to the box office ecosystem.

From Salon • Dec. 10, 2025

“The results are always more significant if the patient and I are alone when the psychosubstantiation tests are performed. External distractions have a deleterious effect on the ramified scores.”

From "Flowers for Algernon" by Daniel Keyes