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

If one deteriorates, the other is almost certain to do so as well, with deleterious consequences.

From Barron's • Mar. 7, 2026

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

From Science Daily • Dec. 24, 2025

This week Dahlia spoke about the deleterious effects of these actions on voting rights with Maya Wiley, president and CEO of The Leadership Conference on Civil and Human Rights.

From Slate • Jul. 26, 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