It will come as no surprise that fallacious is related to the noun fallacy, meaning “delusion” or “falsehood.” Both words come from the Latin word fallacia, which in turn comes from fallere, meaning …

FALLACIOUS definition: containing a fallacy; logically unsound. See examples of fallacious used in a sentence.

The most common fallacious argument is that current climate change must be natural because climate has changed naturally in the past.

If an idea, argument, or reason is fallacious, it is wrong because it is based on a fallacy.

1. Containing or based on a fallacy: a fallacious assumption. 2. Tending to mislead; deceptive: fallacious testimony.

Definition of fallacious adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.

Sep 10, 2025 · There is a widely diffused notion that among all specimens of animal creation man alone possesses any glimmering of reason. This notion is largely fallacious. It is one of those ideas, based …

fallacious, adj. meanings, etymology, pronunciation and more in the Oxford English Dictionary

Britannica Dictionary definition of FALLACIOUS [more fallacious; most fallacious] formal : containing a mistake : not true or accurate a fallacious [= false] set of assumptions fallacious [= misleading] …

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.