Ostensibly valid, but not actually valid.

Roget 495: erroneous, untrue, false, devoid of truth, fallacious, apocryphal, unreal, ungrounded, groundless; unsubstantial etc. 4; heretical etc. (heterodox) 984; unsound; illogical etc. 477.    inexact, unexact inaccurate^†, incorrect; indefinite etc. (uncertain) 475.    illusive, illusory; delusive; mock, ideal etc. (imaginary) 515; spurious etc. 545; deceitful etc. 544; perverted.    controvertible, unsustainable; unauthenticated, untrustworthy.    exploded, refuted; discarded.    in error, under an error etc. n.; mistaken etc. v.; tripping etc. v.; out, out in one's reckoning; aberrant; beside the mark, wide of the mark, wide of the truth, way off, far off; astray etc. (at fault) 475; on a false scent, on the wrong scent; in the wrong box, outside the ballpark; at cross purposes, all in the wrong; all out.    ... show more

Roget 544: false, deceitful, mendacious, unveracious, fraudulent, dishonest, faithless, truthless, trothless; unfair, uncandid; hollow-hearted; evasive; uningenuous, disingenuous; hollow, sincere, Parthis mendacior; forsworn.    artificial, contrived; canting; hypocritical, jesuitical, pharisaical; tartuffish; Machiavelian; double, double tongued, double faced, double handed, double minded, double hearted, double dealing; Janus faced; smooth-faced, smooth spoken, smooth tongued; plausible; mealy-mouthed; affected etc. 855.    collusive, collusory; artful etc. (cunning) 702; perfidious etc. 940; spurious etc. (deceptive) 545; untrue etc. 546; falsified etc. v.; covinous.    ... show more

Roget 545: deceived etc. v.; deceiving &c.; cunning etc. 702; prestigious^†, prestigiatory^†; deceptive, deceptious^†; deceitful, covinous^†; delusive, delusory; illusive, illusory; elusive, insidious, ad captandum vulgus [Lat.].    untrue etc. 546; mock, sham, make-believe, counterfeit, snide [Slang], pseudo, spurious, supposititious, so-called, pretended, feigned, trumped up, bogus, scamped, fraudulent, tricky, factitious bastard; surreptitious, illegitimate, contraband, adulterated, sophisticated; unsound, rotten at the core; colorable; disguised; meretricious, tinsel, pinchbeck, plated; catchpenny; Brummagem.    artificial, synthetic, ersatz [G.]; simulated etc. 544.    ... show more

Roget 925: undue; unlawful etc. (illegal) 964; unconstitutional; illicit; unauthorized, unwarranted, disallowed, unallowed^†, unsanctioned, unjustified; unentitled^†, disentitled, unqualified, disqualified; unprivileged, unchartered.    illegitimate, bastard, spurious, supposititious, false; usurped.    tortious [Law].    undeserved, unmerited, unearned; unfulfilled.    forfeited, disfranchised.    improper; unmeet, unfit, unbefitting, unseemly; unbecoming, misbecoming^†; seemless^†; contra bonos mores [Lat.]; not the thing, out of the question, not to be thought of; preposterous, pretentious, would-be.    ... show more

Plausible but false:
— Spurious inferences.

synonym: specious.

Born out of wedlock:
— The dominions of both rulers passed away to their spurious or doubtful offspring.

synonyms: bastardly, misbegot, misbegotten.

Polish: nieślubny, nieprawy

False or fake; not what it appears to be:
— A spurious work of art.

synonyms: inauthentic, unauthentic.