pernicious

adjective

per·​ni·​cious pər-ˈni-shəs 

1

: highly damaging or destructive often in a way that is not easily seen or noticed

the pernicious influence of corruption

The study highlights just how pernicious this metal can be, even at low levels.

—Bradley Allf

2

archaic : wicked

… two pernicious daughters …

—William Shakespeare

perniciously adverb

perniciousness noun

Did you know?

insidious, sinister, or pernicious?

Few would choose to be associated with people or things that are insidious, sinister, or pernicious; all three of these words have decidedly unpleasant meanings, each with its own particular shade of nastiness.

Insidious comes from a Latin word for “ambush” (insidiae), which is fitting, as this word often carries the meanings “deceitful,” “stealthy,” or “harmful in an imperceptible fashion.” The first two meanings may be applied to people or things (“an insidious enemy,” “an insidious plot”), while the last is usually applied to things (“insidious problems,” “insidious sexism”), in particular to the gradual progress of a disease (“an insidious malignancy”).

Sinister comes from a Latin word meaning “on the left side, unlucky, inauspicious.” Although it is commonly used today in the sense “evil” (“a sinister cult leader”; “a sinister plot”), it may also suggest an ominous foreshadowing of some unfavorable turn of events (“a sinister omen”).

Pernicious has largely stayed true to its etymological root, the Latin noun pernicies “ruin, destruction.” Its original meaning in English, “highly injurious or destructive,” usually applies to things (“pernicious apathy,” “pernicious effects”) and medical conditions (“pernicious fever,” “pernicious anemia”). When applied to people, pernicious means “wicked.”

Synonyms of pernicious

• harmful
• dangerous
• detrimental
• damaging
• adverse

Choose the Right Synonym for pernicious

pernicious, baneful, noxious, deleterious, detrimental mean exceedingly harmful.

pernicious implies irreparable harm done through evil or insidious corrupting or undermining.

the claim that pornography has a pernicious effect on society

baneful implies injury through poisoning or destroying.

the baneful notion that discipline destroys creativity

noxious applies to what is both offensive and injurious to the health of a body or mind.

noxious chemical fumes

deleterious applies to what has an often unsuspected harmful effect.

a diet found to have deleterious effects

detrimental implies obvious harmfulness to something specified.

the detrimental effects of excessive drinking

Examples of pernicious in a Sentence

The notion that poll data are a legitimate form of news has to be one of the most pernicious tenets of late-twentieth-century American journalism … —Barbara Ehrenreich, Nation, 20 Nov. 1995

The more it [the Papacy] took part in the temporal conflicts with consistently pernicious result, the more impotent among the monarchs it revealed itself … —Barbara W. Tuchman, The March of Folly, 1984

At its most pernicious, paper entrepreneurialism involves little more than imposing losses on others for the sake of short-term profits for the firm. —Robert B. Reich, Atlantic, March 1983

More pernicious still has been the acceptance of the author's controversial ideas by the general public.

the pernicious effects of jealousy

She thinks television has a pernicious influence on our children.

Recent Examples on the Web

Unlike the branching corals, which were victims of water that at one point reached hot tub temperatures, pillar coral’s killer was mostly a pernicious and little understood coral disease, story coral tissue loss disease, although extreme heat did claim some. —Alex Harris, Miami Herald, 24 Oct. 2025

Worse, many engaged in a particularly rash form of gaming, making high-speed wagers on in-game action — a pernicious new product called microbetting. —Paul Solotaroff, Rolling Stone, 12 Oct. 2025

Yet his film, even in its omissions, brims with strategic ingenuity and daring, cinematic and political—to fight other films’ empty fantasies with substantial ones, to battle other advocates’ pernicious myths with virtuous ones. —Richard Brody, New Yorker, 7 Oct. 2025

But such ads have been shown to support pernicious behaviors and beliefs around food, exercise and body image. —Mallary Tenore Tarpley, USA Today, 22 Sep. 2025

Word History

Etymology

Middle English, from Anglo-French, from Latin perniciosus, from pernicies destruction, from per- + nec-, nex violent death — more at noxious

First Known Use

15th century, in the meaning defined at sense 1

Phrases Containing pernicious

• pernicious anemia

Rhymes for pernicious

• adventitious
• cementitious
• expeditious
• inauspicious
• injudicious
• meretricious
• repetitious
• superstitious
• surreptitious
• unambitious
• unpropitious
• unsuspicious

Kids Definition

pernicious

adjective

per·​ni·​cious pər-ˈnish-əs 

: very destructive or harmful

a pernicious disease

perniciously adverb

Medical Definition

pernicious

adjective

per·​ni·​cious pər-ˈnish-əs 

: highly injurious or destructive : tending to a fatal issue : deadly

pernicious disease