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irrational Line breaks: ir|ration¦al
Pronunciation: /ɪˈraʃ(ə)n(ə)l/

Definition of irrational in English:


1Not logical or reasonable: irrational feelings of hostility
More example sentences
  • Power sets the guidelines by which we measure what is reasonable and what is irrational.
  • The more irrational and illogical someone becomes, the more logical and incisive I become.
  • By absurd, I do not mean silly, but absurd as is in the illogical or irrational.
unreasonable, illogical, groundless, baseless, unfounded, unjustifiable, unsound;
untenable, implausible, unscientific, arbitrary
informal crazy, mad
British informal barmy, daft
1.1Not endowed with the power of reason.
Example sentences
  • Whenever you encounter a system that seems so irrational, you should ponder what's going on beneath the surface.
  • Man is an irrational being, morals are irrational, and have no metaphysical foundation which make them "real" or worth paying any attention to.
2 Mathematics (Of a number, quantity, or expression) not expressible as a ratio of two integers, and having an infinite and non-recurring expansion when expressed as a decimal. Examples of irrational numbers are the number π and the square root of 2.
Example sentences
  • What about a seed angle derived from the golden ratio, an irrational number?
  • The square root of 2 is an irrational number because it can't be written as a ratio of two integers.
  • How can mathematical concepts like points, infinitesimally small quantities, or irrational numbers be anything but products of our minds?


Mathematics Back to top  
An irrational number or quantity; a surd.
Example sentences
  • Eudoxus's definition of equal ratios corresponds exactly to the modern theory of irrationals.
  • Whether such quirks in the irregularity of irrationals have any implications for number theory remains an open question for mathematicians.
  • His commentary to Euclid is of interest because of its discussion of unordered irrationals.


(also irrationalise) verb
Example sentences
  • When one thinks of planar travel the mind can often be boggled, confused, deceived and irrationalized.
  • The absence of knowledge affects human behaviour by reducing, distorting, and irrationalising the choices made by individuals.
  • I have reason to believe that she is about to irrationalize thinking on every issue.


Late Middle English: from Latin irrationalis, from in- 'not' + rationalis (see rational).

Words that rhyme with irrational

national, passional, rational
Definition of irrational in:
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