Without a basis in reason or fact:
— The allegations proved groundless.

synonyms: baseless, idle, unfounded, unwarranted, wild.

Roget 4: unsubstantial; baseless, groundless; ungrounded; without foundation, having no foundation.    visionary etc. (imaginary) 515; immaterial etc. 137; spectral etc. 980; dreamy; shadowy; ethereal, airy; cloud built, cloud formed; gossamery, illusory, insubstantial, unreal.    vacant, vacuous; empty etc. 187; eviscerated; blank, hollow; nominal; null; inane.    ... show more

Roget 477: 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 [Lat.], it does not follow.    deceptive, sophistical, jesuitical; illusive, illusory; specious, hollow, plausible, ad captandum [Lat.], evasive; irrelevant etc. 10.    weak, feeble, poor, flimsy, loose, vague.    irrational; nonsensical etc. (absurd) 497.    foolish etc. (imbecile) 499; frivolous, pettifogging, quibbling; finespun^†, overrefined^†.    at the end of one's tether, au bout de son latin.    ... show more

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

Polish: bezzasadny, bezpodstawny, nieuzasadniony, niezasadny