Source : Webster's Revised Unabridged Dictionary (1913)

Fallacious \Fal*la"cious\, a. [L. fallaciosus, fr. fallacia: cf.
   F. fallacieux. See {Fallacy}.]
   Embodying or pertaining to a fallacy; illogical; fitted to
   deceive; misleading; delusive; as, fallacious arguments or
   reasoning. -- {Fal*la"cious*ly}, adv. -{Fal*la"cious*ness},
   n.

Source : WordNet®

fallacious
     adj 1: containing or based on a fallacy; "fallacious reasoning";
            "an unsound argument" [syn: {unsound}]
     2: intended to deceive; "deceitful advertising"; "fallacious
        testimony"; "smooth, shining, and deceitful as thin ice" -
        S.T.Coleridge; "a fraudulent scheme to escape paying
        taxes" [syn: {deceitful}, {fraudulent}]
     3: based on an incorrect or misleading notion or information;
        "fallacious hope"