Irrational
Pronunciation : Ir*ra"tion*al
Part of Speech : a.
Etymology : [L. irrationalis: cf. F. irrationnel. See In- not, and Rational.]
Definition : 1. Not rational; void of reason or understanding; as, brutes are irrational animals.
2. Not according to reason; absurd; foolish. It seemed utterly irrational any longer to maintain it. I. Taylor.
3. (Math.)
Defn: Not capable of being exactly expressed by an integral number, or by a vulgar fraction; surd; -- said especially of roots. See Surd.
Syn. -- Absurd; foolish; preposterous; unreasonable; senseless. See Absurd.
Source : Webster's Unabridged Dictionary, 1913