deleterious
- 01 C1 Advanced
harmful to someone or something, often in a slow or hidden way.
causing harm or damage, particularly in a subtle, cumulative, or unexpected manner.
Simple“Smoking has a deleterious effect on your long-term health.”
In context“The new policy had a deleterious impact on staff morale, leading to a significant decrease in productivity over the following quarter.”
UsageFrequently used in the phrase 'deleterious effect' or 'deleterious impact'.
Teacher's tipThis is a high-level academic synonym for 'harmful'; students should use it in formal essays rather than casual conversation.
SynonymsAntonyms - 02 C2 Proficiency
describing a gene or trait that makes a living thing less healthy or less likely to survive.
reducing the biological fitness of an organism; specifically used for mutations that are harmful to survival or reproduction.
Simple“The animal carried a deleterious mutation that made it difficult to find food.”
In context“Natural selection typically acts to remove deleterious alleles from the population, though some may persist in recessive forms.”
UsageCommonly modifies nouns like 'mutation', 'gene', or 'allele'.
Teacher's tipThis sense is specific to biology and genetics; it is rarely encountered outside of scientific literature.
SynonymsmaladaptiveAntonyms
Usage deleterious effect
“The powerless conditions have led to food lines, closed businesses, dead phones, no schools, spoiled food, dirty clothes, dry gas pumps and a multitude of other deleterious effects on life without energy.”
“But I have had an at best ambivalent – and at worst deleterious – relationship with two social media platforms that I’ve had to quit cold turkey.”
Adapted borrowing (1640s; 1582 as deletorious) of New Latin dēlētērius, dēlētōrius + -ous, from Ancient Greek δηλητήριος (dēlētḗrios, “noxious, deleterious”), from δηλητήρ (dēlētḗr, “a destroyer”), from δηλέομαι (dēléomai, “I hurt, damage, spoil, waste”). Not related to delete or deleble. Doublet of deletery.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.