'irrational' definitions:

Definition of 'irrational'

From: WordNet
adjective
Not consistent with or using reason; "irrational fears"; "irrational animals" [ant: rational]
adjective
Real but not expressible as the quotient of two integers; "irrational numbers" [ant: rational]
noun
A real number that cannot be expressed as a rational number [syn: irrational number, irrational]

Definition of 'irrational'

From: GCIDE
  • irrational \ir*ra"tion*al\ ([i^]r*r[a^]sh"[u^]n*al), a. [L. irrationalis: cf. F. irrationnel. See In- not, and Rational.] [1913 Webster]
  • 1. Not rational; void of reason or understanding; as, brutes are irrational animals. [1913 Webster]
  • 2. Not according to reason; having no rational basis; clearly contrary to reason; easily disproved by reasoning; absurd; -- of assertions and beliefs. Hence, of actions: foolish; unreasonable. [1913 Webster +PJC]
  • It seemed utterly irrational any longer to maintain it. --I. Taylor. [1913 Webster]
  • 3. (Math.) Not capable of being exactly expressed by an integral number, nor by a ratio of integral numbers; surd; -- said especially of roots. See Surd.
  • Syn: Absurd; foolish; preposterous; unreasonable; senseless. See Absurd. [1913 Webster]

Synonyms of 'irrational'

From: Moby Thesaurus