irrational

adjective
ir·​ra·​tio·​nal | \ i-ˈra-sh(ə-)nəl How to pronounce irrational (audio) , ˌi(r)- \

Definition of irrational

 (Entry 1 of 2)

: not rational: such as
a(1) : lacking usual or normal mental clarity or coherence
(2) : not endowed with reason or understanding
b : not governed by or according to reason irrational fears
c Greek and Latin prosody
(1) of a syllable : having a quantity other than that required by the meter
(2) of a foot : containing such a syllable
d(1) : being an irrational number an irrational root of an equation
(2) : having a numerical value that is an irrational number a length that is irrational

irrational

noun

Definition of irrational (Entry 2 of 2)

1 : an irrational being

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Other Words from irrational

Adjective

irrationality \ i-​ˌra-​shə-​ˈna-​lə-​tē How to pronounce irrational (audio) , ˌi(r)-​ \ noun
irrationally \ i-​ˈra-​sh(ə-​)nə-​lē How to pronounce irrational (audio) , ˌi(r)-​ \ adverb

Examples of irrational in a Sentence

Adjective He became irrational as the fever got worse. She had an irrational fear of cats.
Recent Examples on the Web: Adjective Lots of other technologies—genetic engineering, high-temperature superconductors, nanotechnology and fusion energy come to mind—have gone through phases of irrational exuberance. John Horgan, Scientific American, "Will Quantum Computing Ever Live Up to Its Hype?," 20 Apr. 2021 NFTs have provoked plenty of irrational exuberance, but there is no denying one aspect of their nature: Their authenticity. Michael Spellacy, Forbes, "Authentic Opportunity: Wealth Managers Need A Strategy For Digital Assets," 12 Apr. 2021 Sometimes our thinking can be irrational or illogical. Expert Panel®, Forbes, "Break Out Of The Comfort Zone With These 16 Exercises," 6 Apr. 2021 David Pontius, the victim, had been experiencing a mental health episode and grown violent and irrational, according to witnesses. Michael Ruiz, Fox News, "US Virgin Islands yacht captain whose girlfriend went missing hired Ghislaine Maxwell's lawyer," 27 Mar. 2021 There are two kinds of numbers, rational (numbers that can be expressed as the division of two integers), like 13/20 or 0, and irrational (numbers that cannot), like the square root of 2. Kevin Fisher-paulson, San Francisco Chronicle, "A family as irrational as pi holds on to rational moments," 23 Mar. 2021 Whites were often outnumbered by Blacks in many Southern areas, and feared unfounded and irrational threats dreamed up by powerful, partisan local newspapers. CNN, "The Capitol riot is an eerie repeat of this tense era in American history," 3 Mar. 2021 More than a century after Freud abandoned his own scientific project, returning to his work may seem somehow irrational. Washington Post, "A brain researcher on what Freud got right," 26 Feb. 2021 Like many of my patients, Mrs. Gomes isn’t being unreasonable or irrational. Jay Baruch, STAT, "As a doctor in the Covid-19 era, I’ve learned that judging patients’ decisions comes easier than it should," 31 Dec. 2020 Recent Examples on the Web: Noun We are all steered by a mixture of the rational and the irrational. Christopher Beha, Harpers Magazine, "A Novel Approach," 5 Jan. 2021 In the battle between the infinitely large and the infinitely small, Dirichlet had to find the right balance to prevent some irrationals from slipping through the cracks. Quanta Magazine, "How Rational Math Catches Slippery Irrational Numbers," 10 Mar. 2020 These unwieldy numbers have plagued mathematicians since the ancient Greeks; indeed, legend has it that Hippasus was drowned for suggesting irrationals existed. Leila Sloman, Scientific American, "New Proof Solves 80-Year-Old Irrational Number Problem," 16 Sep. 2019 Instead, mathematicians ask about the proportion of the total number of irrationals corralled by each fraction. Quanta Magazine, "New Proof Settles How to Approximate Numbers Like Pi," 14 Aug. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'irrational.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of irrational

Adjective

14th century, in the meaning defined above

Noun

1646, in the meaning defined at sense 1

History and Etymology for irrational

Adjective

Middle English, from Latin irrationalis, from in- + rationalis rational

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Time Traveler for irrational

Time Traveler

The first known use of irrational was in the 14th century

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Statistics for irrational

Last Updated

29 Apr 2021

Cite this Entry

“Irrational.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/irrational. Accessed 9 May. 2021.

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More Definitions for irrational

irrational

adjective

English Language Learners Definition of irrational

: not thinking clearly : not able to use reason or good judgment
: not based on reason, good judgment, or clear thinking

irrational

adjective
ir·​ra·​tio·​nal | \ i-ˈra-shə-nᵊl How to pronounce irrational (audio) \

Kids Definition of irrational

1 : not able to reason The fever made him irrational.
2 : not based on reason irrational fears

Other Words from irrational

irrationally adverb

irrational

adjective
ir·​ra·​tio·​nal | \ (ˈ)ir-ˈ(r)ash-nəl, -ən-ᵊl How to pronounce irrational (audio) \

Medical Definition of irrational

: not rational: as
a : lacking usual or normal mental clarity or coherence was irrational for several days after the accident
b : not governed by or according to reason irrational fears

Other Words from irrational

irrationality \ (ˌ)ir-​ˌ(r)ash-​ə-​ˈnal-​ət-​ē How to pronounce irrational (audio) \ noun, plural irrationalities
irrationally \ (ˈ)ir-​ˈ(r)ash-​nə-​lē, -​ən-​ᵊl-​ē How to pronounce irrational (audio) \ adverb

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irrational

adjective
ir·​ra·​tio·​nal | \ ir-ˈra-shə-nəl How to pronounce irrational (audio) \

Legal Definition of irrational

: not rational: as
a : not governed by reason, mental clarity, or understanding
b : not governed by a fair consideration of facts or evidence broadly : arbitrary an irrational decision to deny the permit

Other Words from irrational

irrationality \ ir-​ˌra-​shə-​ˈna-​lə-​tē How to pronounce irrational (audio) \ noun
irrationally adverb

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Comments on irrational

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