1. (a.) Destitute of reason; as, a reasonless man or mind.

2. (a.) Void of reason; not warranted or supported by reason; unreasonable.

abnormal absonant arbitrary batty bedlamite bereft of reason brainless brainsick capricious careless contradictory contrary to reason crackbrained cracked crazed crazy daft deluded demented deprived of reason deranged disoriented distraught fallacious faulty flawed flighty foolish hallucinated headless heedless ignorant ill-advised ill-considered ill-contrived ill-devised ill-gauged ill-judged illogical impolitic imprudent inadvertent inadvisable inauthentic inconclusive incongruous inconsequent inconsequential inconsiderate inconsistent indiscreet inept inexpedient injudicious insane insensate invalid irrational lackbrained lean-minded lean-witted loco loose lunatic mad maddened manic mazed mental mentally deficient meshuggah mindless misadvised misguided moon-struck myopic non compos non compos mentis nonrational nonscientific not all there not bright not following not right odd of little brain of unsound mind off paralogical pea-brained pin-brained psycho queer reckless self-annulling self-contradictory self-refuting senseless shortsighted sick slackminded slackwitted sophistic stark-mad stark-staring mad strange tetched thoughtless touched unadvised unauthentic unbalanced uncalculating unconnected unconsidered undiscerning unforeseeing ungifted unguarded unhinged unintellectual unintelligent unphilosophical unreasonable unreasoning unreflecting unreflective unsane unscientific unseeing unsensible unsettled unsound untalented unthinking unthoughtful unwise wandering without reason witless