1 : embodying a fallacy
2 : tending to deceive or mislead : delusive
The notion that disease is caused by malign spirits was known to be fallacious long before germ theory gave us real understanding of disease.
"The whole idea that Romney was responsible for good or bad things in Massachusetts is fallacious - just as it is fallacious that any executive is responsible for the ups and downs of the economy." - University of Michigan political scientist Michael Heaney as quoted by Seth McLaughlin in an article in The Washington Times, February 27, 2012
Did You Know?
"Oh what a tangled web we weave / When first we practise to deceive!" So wrote Sir Walter Scott in his 1808 poem Marmion. Scott’s line wasn't written with etymology in mind, but it might be applied to the history of "fallacious." That word traces back to the Latin verb "fallere" ("to deceive"), but it passed through a tangle of Latin and French forms before it eventually made its way into English in the early 1500s. Other descendants of "fallere" in English include "fail," "false," and "fault."
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Word Family Quiz
What relative of "fallacious" means "capable of making a mistake"? The answer is ...