• Damaging or destructive, especially if in a way that is covert or difficult to perceive

  • Fatal


Most of us are good at avoiding the things that are clearly bad for us, but truly pernicious harms often come from choices or situations whose negative consequences are not immediately discernible. That’s exactly what makes them so diabolical — there’s no way to avoid what we can’t perceive. Healthy skepticism can help, but usually the best we can do is accept that, at some point, everyone has to deal with something pernicious.

If something is pernicious, it is harmful or even ruinous, oftentimes in a way that is difficult to see at first. While anything that produces extremely negative repercussions can be characterized as pernicious, the word is especially appropriate for describing something with ill effects that are subtle or insidious. Sure, a parking ticket would certainly be pernicious to your finances, but getting cheated by an email scam? That would be a pernicious misfortune. The ticket has a clear impact on your finances, since it’s sitting on your car’s windshield, but you might not realize how much you lost to that “Nigerian prince” until you carefully scrutinize your next bill.

The word can also specifically distinguish something as fatal, as in a pernicious disease, a pernicious lightning strike, or a pernicious rattlesnake bite.

You can also use pernicious to characterize people as wicked or deceitful. Calling people pernicious implies that they have little regard for morals and are willing to harm others to get what they want. This is an old-fashioned meaning of pernicious that’s rarely used today, but it would still be apt for describing someone like a mass murderer or a tyrannical warlord.

Example: The uncomfortable new uniforms had a pernicious effect on employee morale.

Example: She never stopped smoking, though she knew it would prove a pernicious habit.

Example: We learned too late the pernicious effect that factory waste was having on our local water supply.

Example: In each story, the hero foils the evil plot of a pernicious villain.


Pernicious comes from the Latin word pernicies, a noun which means “annihilation” or “destruction.” Pernicies comprises the prefix per-, meaning “because of” or “from,” and necis, meaning “murder.” We can trace necis even further back to the Proto-Indo-European root nek-, which means “death.” That root is also the source of many other common English words, including necromancy, noxious, and — go figure — nectar.

Back to pernicies, though, which would inspire first the Latin perniciosus, meaning “damaging,” and later the Middle French pernicios, meaning “injurious” or “hurtful.” Those words are the closest relatives of pernicious, which finally arrived in English in the early 1400s.

Derivative Words

Perniciously: This adverb form of pernicious denotes when a verb, adjective, or other adverb is related to destructiveness or deadliness.

Example: He insisted on eating his lunch at his desk every afternoon, perniciously dropping crumbs into his keyboard.

Example: The virus spread perniciously quickly.

Perniciousness: Perniciousness is a noun that refers to the qualities of being destructive or lethal.

Example: She would wash her car after every storm, concerned about the perniciousness of mineral buildup on the wax finish.

Example: The perniciousness of not wearing a seatbelt in a car is common sense.

In Literature

From Adam Smith’s The Wealth of Nations:

Our merchants and masters complain much of the bad effects of high wages in raising the price and lessening the sale of goods. They say nothing concerning the bad effects of high profits. They are silent with regard to the pernicious effects of their own gains. They complain only of those of other people.

In this passage, Smith refers to the destructive, or pernicious, economic effects of shortchanging employee wages to inflate profits.


  • Pernicious is viciously harmful.

  • Perjury is pernicious toward the pursuit of truth.


Consequences, Cause, Effect, Pain, Injury, Death, Deadly, Fatal, Murder

Bring out the linguist in you! What is your own interpretation of pernicious. Did you use pernicious in a game? Provide an example sentence or a literary quote.