What does deleterious mean?
"Deleterious" is a formal adjective meaning harmful or damaging, particularly in ways that are gradual, cumulative, or not immediately obvious. It derives from the Greek "dēlētērios," rooted in a verb meaning to destroy or wear away, and entered English in the early seventeenth century. The word is most frequently encountered in scientific, medical, and academic contexts, where writers describe the deleterious effects of smoking, pollution, stress, or poor nutrition on health. It typically pairs with nouns such as "effect," "consequence," and "influence," and it often implies insidious harm — damage that accumulates quietly rather than striking at once. Because of its precise and slightly clinical tone, "deleterious" is favored over plainer words like "bad" when the writer wants to convey measured, authoritative judgment. It should not be confused with "delete," despite the shared-looking spelling; the resemblance is coincidental in modern usage. Knowing this word allows speakers to describe subtle harms with accuracy and elegance.
adjectiveCausing harm or damage, especially in a gradual or subtle way.
- Causing harm or damage; injurious, especially in a gradual or subtle manner.
"The deleterious effects of prolonged stress on the immune system are well documented."
"Smoking has a deleterious effect on lung function."
"Critics argued that the new policy would be deleterious to small businesses."
Though it sounds like something you'd press on a keyboard, "deleterious" has nothing to do with deleting — it comes from a Greek root meaning to wear away, like slow-acting poison.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of deleterious
"Deleterious" derives from the Greek "dēlētērios," meaning destructive or deadly, from "dēleisthai," to harm or destroy. The word passed into Latin as "deleterius" before entering English in the early seventeenth century. It shares its Greek root with the rarer English word "deletery," meaning destructive, and is unrelated etymologically to the verb "delete."
Related word forms
How deleterious is actually used
"Deleterious" is a formal word common in academic, scientific, medical, and legal writing. It typically appears attributively before nouns such as "effect," "impact," or "consequence," and often carries the implication of gradual or cumulative damage rather than immediate destruction.
Easily confused with deleterious
"Deletive" means having the power to delete or erase, while "deleterious" means causing harm or damage.