an incorrect or misleading notion or opinion based on inaccurate facts or invalid reasoning unsound or invalid reasoning the tendency to mislead an error in reasoning that renders an argument logically invalid
WordReference Random House Learner's Dictionary of American English © 2025
fal•la•cy /ˈfæləsi/USA pronunciation
n., pl. -cies.
WordReference Random House Unabridged Dictionary of American English © 2025- a deceptive, misleading, or false notion;
misconception:[countable]It's a fallacy to think that government will solve all our problems. - Philosophy faulty or erroneous reasoning:[uncountable]The statement was based on fallacy.
- a misleading or unsound argument:[countable]A good logician would see the fallacies in your reasoning.
fal•la•cy
(fal′ə sē),USA pronunciation n., pl. -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. - Philosophy[Logic.]any of various types of erroneous reasoning that render arguments logically unsound.
- [Obs.]deception.
- Middle French
- Latin fallācia a trick, deceit, equivalent. to fallāc- (stem of fallāx) deceitful, fallacious + -ia -y3; replacing Middle English fallace
- 1350–1400
- 1.See corresponding entry in Unabridged misconception, delusion, misapprehension.
Collins Concise English Dictionary © HarperCollins Publishers::
'fallacy' also found in these entries (note: many are not synonyms or translations):