fallacious

American  

[fuh-ley-shuhs] / fəˈleɪ ʃəs /

adjective

1. containing a fallacy; logically unsound.

   fallacious arguments.

2. deceptive; misleading.

   fallacious testimony.

3. disappointing; delusive.

   a fallacious peace.

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fallacious British  

/ fəˈleɪʃəs /

adjective

1. containing or involving a fallacy; illogical; erroneous

2. tending to mislead

3. delusive or disappointing

   a fallacious hope

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Other Word Forms

• fallaciously adverb
• fallaciousness noun
• nonfallacious adjective
• nonfallaciously adverb
• nonfallaciousness noun
• unfallacious adjective
• unfallaciously adverb

Etymology

Origin of fallacious

First recorded in 1500–10, fallacious is from the Latin word fallāciōsus deceitful, deceptive. See fallacy, -ous

Explanation

Something fallacious is a mistake that comes from too little information or unsound sources. Predictions that the whole state of California will snap off from the rest of North America and float away have proven to be fallacious — for now, anyway. Fallacious comes ultimately from the Latin fallax, "deceptive." The word fallacious might describe an intentional deception or a false conclusion coming from bad science or incomplete understanding. A tween's assumption that anyone over 20 can't understand her situation would be fallacious; we have all been young once too.

Example Sentences

For Sermitsiaq editor Masaana, the rhetoric from the US is pushing a fallacious binary choice.

From BBC • Jan. 7, 2026

He argued that the constitutional change had reset the clock to zero, but legal experts in Senegal and abroad dismissed the contention as fallacious.

From New York Times • Jul. 3, 2023

It also took home the big award for worst picture, with the Atlanta Reporter calling it “a showy exercise in exploitation and fallacious storytelling” while reviewer Jorge Rivera Rubio dubbed it “trauma porn.”

From Los Angeles Times • Mar. 13, 2023

“Everything would be taken to be shredded in due course. … The document was taken when I was not there and leaked out of context, helping to fuel fallacious narratives against me.”

From Washington Post • Jan. 12, 2023

Let me end, then, with a couple of additional bad inferences which are further suggestive of the role that innumeracy—in the guise of fallacious logic—plays in pseudoscience.

From "Innumeracy: Mathematical Illiteracy and Its Consequences" by John Allen Paulos