fallacy

[ fal-uh-see ]
/ ˈfæl ə si /

noun, plural fal·la·cies.

a deceptive, misleading, or false notion, belief, etc.: That the world is flat was at one time a popular fallacy.
a misleading or unsound argument.
deceptive, misleading, or false nature; erroneousness.
Logic. any of various types of erroneous reasoning that render arguments logically unsound.
Obsolete. deception.

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Origin of fallacy

1350–1400; <Latin fallācia a trick, deceit, equivalent to fallāc- (stem of fallāx) deceitful, fallacious + -ia-y3; replacing Middle English fallace<Middle French
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Example sentences from the Web for fallacy

British Dictionary definitions for fallacy

fallacy
/ (ˈfæləsɪ) /

noun plural -cies

an incorrect or misleading notion or opinion based on inaccurate facts or invalid reasoning
unsound or invalid reasoning
the tendency to mislead
logic an error in reasoning that renders an argument logically invalid

Word Origin for fallacy

C15: from Latin fallācia, from fallax deceitful, from fallere to deceive
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Cultural definitions for fallacy

fallacy

A false or mistaken idea based on faulty knowledge or reasoning. For example, kings who have divorced their wives for failing to produce a son have held to the fallacy that a mother determines the sex of a child, when actually the father does. (See sex chromosomes.)

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.