Adjective

• S: (adj) fallacious, unsound (containing or based on a fallacy) "fallacious reasoning"; "an unsound argument"
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• antonym
• S: (adj) deceitful, fallacious, fraudulent (intended to deceive) "deceitful advertising"; "fallacious testimony"; "smooth, shining, and deceitful as thin ice" - S.T.Coleridge; "a fraudulent scheme to escape paying taxes"
• similar to
• derivationally related form
• antonym
• S: (adj) fallacious (based on an incorrect or misleading notion or information) "fallacious hope"