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.

To unquestioningly adhere to traditional policies when there is good reason for change can be regarded as a fallacious appeal to authority.

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.

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

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 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.

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] …