1. fallacious(s = adj.all) unsound - containing or based on a fallacy; "fallacious reasoning"; "an unsound argument"
Derived forms noun fallaciousness1, noun fallacy1
2. fallacious(s = adj.all) deceitful, fraudulent - intended to deceive; "deceitful advertising"; "fallacious testimony"; "smooth, shining, and deceitful as thin ice"; "a fraudulent scheme to escape paying taxes"
3. fallacious(s = adj.all) Array - based on an incorrect or misleading notion or information; "fallacious hope"
Derived form noun fallaciousness1
Embodying or pertaining to a fallacy; illogical; fitted to deceive; misleading; delusive; as, fallacious arguments or reasoning. [1913 Webster]
N intuition, instinct, association, hunch, gut feeling, presentiment, premonition, rule of thumb, superstition, astrology, faith (supposition), sophistry, paralogy, perversion, casuistry, jesuitry, equivocation, evasion, chicane, chicanery, quiddet, quiddity, mystification, special pleading, speciousness, nonsense, word sense, tongue sense, false reasoning, vicious reasoning, circular reasoning, petitio principii, ignoratio elenchi, post hoc ergo propter hoc, non sequitur, ignotum per ignotius, misjudgment, false teaching, sophism, solecism, paralogism, quibble, quirk, elenchus, elench, fallacy, quodlibet, subterfuge, subtlety, quillet, inconsistency, antilogy, a delusion, a mockery, and a snare, claptrap, cant, mere words, lame and impotent conclusion, meshes of sophistry, cobwebs of sophistry, flaw in an argument, weak point, bad case, overrefinement, hairsplitting, intuitive, instinctive, impulsive, independent of reason, anterior to reason, gratuitous, hazarded, unconnected, unreasonable, illogical, false, unsound, invalid, unwarranted, not following, inconsequent, inconsequential, inconsistent, absonous, absonant, unscientific, untenable, inconclusive, incorrect, fallacious, fallible, groundless, unproved, non sequitur, it does not follow, deceptive, sophistical, jesuitical, illusive, illusory, specious, hollow, plausible, ad captandum, evasive, irrelevant, weak, feeble, poor, flimsy, loose, vague, irrational, nonsensical, foolish, frivolous, pettifogging, quibbling, finespun, overrefined, at the end of one's tether, au bout de son latin, intuitively, by intuition, illogically, non constat, that goes for nothing.
N error, fallacy, misconception, misapprehension, misstanding, misunderstanding, inexactness, laxity, misconstruction, miscomputation, non sequitur, mis-statement, mis-report, mumpsimus, mistake, miss, fault, blunder, quiproquo, cross purposes, oversight, misprint, erratum, corrigendum, slip, blot, flaw, loose thread, trip, stumble, botchery, slip of the tongue, slip of the lip, Freudian slip, slip of the pen, lapsus linguae, clerical error, bull, haplography, illusion, delusion, snare, false impression, false idea, bubble, self-decit, self-deception, mists of error, heresy, hallucination, false light, dream, fable, bias, misleading, erroneous, untrue, false, devoid of truth, fallacious, apocryphal, unreal, ungrounded, groundless, unsubstantial, heretical, unsound, illogical, inexact, unexact inaccurate, incorrect, indefinite, illusive, illusory, delusive, mock, ideal, spurious, deceitful, perverted, controvertible, unsustainable, unauthenticated, untrustworthy, exploded, refuted, discarded, in error, under an error, mistaken, tripping, out, out in one's reckoning, aberrant, beside the mark, wide of the mark, wide of the truth, way off, far off, astray, on a false scent, on the wrong scent, in the wrong box, outside the ballpark, at cross purposes, all in the wrong, all out, more or less, errare est humanum, mentis gratissimus error, on the dubious waves of error tost, to err is human, to forgive divine, you lie -- under a mistake.