Yesterday, one of my co-workers read that “perfidious” was the word of the day and he seemed so tickled by it (and its definition) that he inserted it into as many conversations as possible. Today, while I was rifling through my “to do” list for Editor’s Corner, I stumbled serendipitously on this article (unedited text at DailyWritingTips). Charles Roof, for all you do, this one’s for you!
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,” 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.
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. [KC – From Merriam-Webster, “unpleasant and likely to cause bad feelings in other people,” though my mom would tell you that “nobody can make you feel bad—only
you can make you feel bad.” The eight-year-old in me says, “Thanks, Mom!”]
Perfidious means “treacherous” or “disloyal” (the second syllable of this word is cognate with fid- in fidelity); the noun form is perfidy. Pernicious, meanwhile, means deadly. Pernicious anemia is a particularly serious form of blood-cell depletion that might as well be called insidious anemia because of its slow onset.
On that note, go forth and enjoy your day!
Kara Church
Senior Technical Editor
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