irrational Meaning, Definition & Usage

  1. noun a real number that cannot be expressed as a rational number
    irrational number.
  2. adjective not consistent with or using reason
    • irrational fears
    • irrational animals
  3. adjective real but not expressible as the quotient of two integers
    • irrational numbers

WordNet

Ir*ra"tion*al adjective
Etymology
L. irrationalis: cf. F. irrationnel. See In- not, and Rational.
Definitions
  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.) 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.

Webster 1913