Definition of irrational in US English:

irrational

adjective

  • 1Not logical or reasonable.

    • ‘He had a very short fuse and he could be totally irrational at times.’
    • ‘Booze and cocaine corroded his sanity and left him with a legacy of irrational behaviour.’
    • ‘I believe that the seemingly irrational logic of the national can still promote everyday alliances and popular mobilizations.’
    • ‘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.’
    • ‘Their hostility towards each other, however, was tangible and frequently led to quite irrational behaviour.’
    • ‘Power sets the guidelines by which we measure what is reasonable and what is irrational.’
    • ‘I am sort of notorious for my utterly irrational fears.’
    • ‘Crowds and mobs are not completely irrational, but they have their own logic.’
    • ‘Home values have soared to high levels in many countries as irrational exuberance grips the markets.’
    • ‘Chris smiled, sure that Seth's fears were completely irrational.’
    • ‘But Delta's seemingly irrational behavior has a very logical explanation.’
    • ‘If it hadn't seemed so irrational, she would have begged him not to go.’
    • ‘Identify and uproot irrational beliefs that lead you to place unrealistic demands on yourself.’
    • ‘She had never known for her daughter to be so irrational, so crazy.’
    • ‘Without that insight, a supplier can encounter fewer surprises by evaluating even seemingly irrational scenarios.’
    • ‘The author of the piece argues that our attitude towards it is mostly irrational prejudice.’
    • ‘I have an irrational dislike of cell phones.’
    • ‘Solutions that would seem logical to us would seem totally irrational to them.’
    • ‘Australians aren't at all used to visceral and irrational hatred directed at them.’
    unreasonable, illogical, groundless, baseless, unfounded, unjustifiable, unsound
    View synonyms
    1. 1.1 Not endowed with the power of reason.
      • ‘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.’
  • 2Mathematics
    (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.

    • ‘A transcendental number is an irrational number that is not a root of any polynomial equation with integer coefficients.’
    • ‘The square root of 2 is an irrational number because it can't be written as a ratio of two integers.’
    • ‘He considered computation with irrational numbers and polynomials to be part of algebra.’
    • ‘What about a seed angle derived from the golden ratio, an irrational number?’
    • ‘How can mathematical concepts like points, infinitesimally small quantities, or irrational numbers be anything but products of our minds?’

noun

Mathematics
  • An irrational number.

    • ‘Eudoxus's definition of equal ratios corresponds exactly to the modern theory of irrationals.’
    • ‘His commentary to Euclid is of interest because of its discussion of unordered irrationals.’
    • ‘Any finite segment can be continued to produce a rational and any finite segment can be continued to produce an irrational.’
    • ‘Whether such quirks in the irregularity of irrationals have any implications for number theory remains an open question for mathematicians.’
    • ‘If we chop off an infinite cfe after a finite number of steps then we will create a rational approximation to the original irrational.’

Origin

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

Pronunciation

irrational

/ɪ(r)ˈræʃ(ə)nəl//i(r)ˈraSH(ə)nəl/