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

Derived Forms

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

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; see -ious

Explanation

If something is deleterious, it does harm or makes things worse. Smoking has obvious deleterious effects on your health, not to mention your social life. My parents were worried that their divorce would have a deleterious effect on us kids, but in the end it was less harmful than watching them fight all the time. For most plants, a lack of sunlight has very deleterious consequences, but there are some plants that actually do very well in the dark. It's a wonder, given how well-established the science is, that we continue to do things that are deleterious to the fragile ecosystem. We must be willing to live with the deleterious effects.

Example Sentences

This leads to dehydration and eventually “desertification”—a phenomenon the film tracks across a quasi-equatorial band of the Earth, where deforestation in pursuit of farmland has had a deleterious effect.

From The Wall Street Journal • Jun. 2, 2026

Demand destruction is among the many deleterious consequences of oil near $100 a barrel, said Pavel Molchanov, investment strategy analyst at Raymond James.

From MarketWatch • Apr. 14, 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

And weight carried around the middle is more deleterious than extra pounds in the butt.

From "Counting by 7s" by Holly Goldberg Sloan