Adjectives

(s)fallacious, unsoundcontaining or based on a fallacy“fallacious reasoning”, “an unsound argument”
(s)deceitful, fallacious, fraudulentinvolving deception“deceitful advertising”, “fallacious testimony”, “smooth, shining, and deceitful as thin ice” (S.T.Coleridge), “a fraudulent scheme to escape paying taxes”
(s)fallaciousbased on an incorrect or misleading notion or information“fallacious hope”