“Insidious” vs. “Invidious”

By Mark Nichol

What’s the difference between insidious and invidious, and what about perfidious and pernicious, for that matter? None of the four words is synonymous with any of the others, though your connotation radar may correctly sense that they all have unpleasant associations.

Insidious, which derives from the Latin word for “ambush” (the second syllable is cognate with sit), means “treacherous” or “seductive,” with an additional connotation of “subtle,” in the sense of a gradual, cumulative effect. (This, unlike the other meanings, is neutral, but the word is rarely used except in a negative sense.) For example, in medical terminology, an insidious disease is one that remains hidden until it is well established. The noun form is insidiousness, and the adverbial form is insidiously.

Invidious, meanwhile, which stems from the Latin word for envy, refers to feelings of animosity, discontent, or resentment, or to obnoxious or even harmful behavior.

Perfidious (the second syllable of this word is cognate with fid- in fidelity) means “treacherous” or “disloyal”; the noun form is perfidy. Pernicious, meanwhile, means deadly. (The second syllable is cognate with nox- in noxious.) Pernicious anemia is a particularly serious form of blood-cell depletion that might as well be called insidious anemia because of its slow onset, and pernicious scale, also known as San Jose scale (for its discovery in the California city of that name), is an insect that infests and kills trees.

The noun and adverbial forms of invidious, perfidious, and pernicious follow the same pattern as those for insidious.

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3 Responses to ““Insidious” vs. “Invidious””

  • Gordon Havens

    This article (and all others based on definitions and distinctions of words) is begging for example sentences. Using each word correctly in a sentence drives the lesson home.

  • thebluebird11

    I learned all these words many years ago, definitely in high school (OK wasn’t that just yesterday?), but don’t come across them often. Since I’m in the medical field, we do use the words insidious and pernicious on a fairly regular basis, the former in conjunction with disease processes and the latter in conjunction with anemia.
    As Gordon mentioned, it would be nice to see some examples of use in sentences (especially the words invidious and perfidious, and their various permutations), and that way maybe I could find creative ways of sneaking them into conversation. I guess maybe I’m lucky I have no perfidious or invidious friends? Still, if I used “perfidious” in a conversation, I would have to explain what it means; that is a waste of time, on top of the fact that it is one more syllable than “disloyal” LOL 😉

  • venqax

    Your behavior is really insidious but not really that invidious.

    Bob is so pernicious! He may soon become perfidious, as well.

    Does that help? 🙂

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