1. (a.) Lacking reason or understanding\; as, brutes are irrational animals.

2. (a.) Not according to reason; absurd; foolish.

3. (a.) Not capable of being exactly expressed by an integral number, or by a vulgar fraction; surd; -- said especially of roots. See Surd.

abnormal absonant algorismic algorithmic aliquot bereft of reason bigoted brainless brainsick cardinal contradictory contrary to reason crackbrained cracked crazed crazy daft decimal deluded demented deprived of reason deranged differential digital disoriented distraught even exponential extravagant extreme extremist fallacious fanatic faulty figural figurate figurative finite flawed flighty foolish fractional haggard hallucinated headless ignorant ill-advised ill-considered ill-contrived ill-devised ill-gauged ill-judged illogical imaginary impair impolitic impossible imprudent inadvisable inauthentic inconclusive incongruous inconsequent inconsequential inconsiderate inconsistent indiscreet inept inexpedient infinite injudicious inordinate insane insensate integral invalid lackbrained lean-minded lean-witted loco logarithmic logometric loose lunatic mad maddened manic mazed mental mentally deficient meshuggah mindless misadvised misguided moon-struck myopic negative non compos non compos mentis nonrational nonscientific not all there not bright not following not right numeral numerary numerative numeric odd of little brain of unsound mind off ordinal overenthusiastic overreligious overzealous pair paralogical pea-brained perfervid pin-brained positive possible prime psycho queer rabid radical rational real reasonless reciprocal reckless self-annulling self-contradictory self-refuting senseless shortsighted sick slackminded slackwitted sophistic stark-mad stark-staring mad strange submultiple surd tetched thoughtless touched transcendental ultrazealous unadvised unauthentic unbalanced unconnected unconsidered undiscerning unforeseeing ungifted unhinged unintellectual unintelligent unphilosophical unreasonable unreasoning unreflecting unreflective unsane unscientific unseeing unsensible unsettled unsound untalented unthinking unthoughtful unwise wandering wild-eyed wild-looking without reason witless zealotic