Definition of irrational in English:


Syllabification: ir·ra·tion·al
Pronunciation: /iˈraSHənl


  • 1Not logical or reasonable.
    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; absurd, ridiculous, ludicrous, preposterous, silly, foolish, senseless
  • 1.1Not endowed with the power of reason.
    More 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 nonrecurring expansion when expressed as a decimal. Examples of irrational numbers are the number π and the square root of 2.
    More 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.
    More 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.



Pronunciation: /iˌraSHəˈnalitē/
More example sentences
  • The bitterness and irrationality of the thought frightened me, and I did my best to push it away.
  • It would seem that the accused also has to accept his victim's phobias, irrationality or stupidity.
  • The ending of the film suggests that rationality and irrationality are interchangeable and not very far apart from one another.


More 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.


More example sentences
  • I felt quite irrationally pleased with myself, as though I had actually achieved something.
  • Funny how perfectly rational people behave irrationally in times of war.
  • He is at times inspiringly Japanese, then suddenly, completely and irrationally unconventional.


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

More definitions of irrational

Definition of irrational in:

Get more from Oxford Dictionaries

Subscribe to remove adverts and access premium resources

Word of the day kerf
Pronunciation: kəːf
a slit made by cutting with a saw