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 irrationality (audio) , ˌi(r)-​ \ noun
irrationally \ i-​ˈra-​sh(ə-​)nə-​lē How to pronounce irrationally (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 But the line between protection and accommodation of unhealthy and irrational behaviors can be a slippery slope. Elissa Strauss, CNN, "How parents shape their children's mental health," 4 Oct. 2020 Choosing to click on a link promising to show Covid case numbers in your state isn’t a completely irrational decision. Sonner Kehrt, Wired, "The Cyber-Avengers Protecting Hospitals From Ransomware," 29 Sep. 2020 TiKTok’s legal team argued at an unusual Sunday hearing that the ban was irrational, as ByteDance is still trying to strike the divestiture deal that Trump demanded in order not to ban the app. David Meyer, Fortune, "Fortune’s latest list celebrates the startups tackling society’s big problems," 28 Sep. 2020 Even well-meaning people can make mistakes or fix on irrational things. Washington Post, "Carolyn Hax: His anxiety is causing distress for his partner," 25 Sep. 2020 Yes, this chicken soup’s mini meatballs and teeny-tiny pasta elicit a (possibly) irrational joy in me, like dollhouse furniture or matchstick carvings. Kathleen Squires, WSJ, "Recipe for a Uniquely Uplifting Chicken Soup," 23 Sep. 2020 Behavioral finance is a field that examines how people make decisions, with special attention to irrational ones. Russ Wiles, The Arizona Republic, "Emotions can mess up an investment plan. Beware of 6 irrational ways to make decisions," 20 Sep. 2020 Some of that exuberance is starting to look irrational. Noah Buhayar, Bloomberg.com, "Rents Sink Toward Reset Moment in Cities With Smoke-Filled Skies," 16 Sep. 2020 The Fed has rescued financial markets, and while its policies have also encouraged some irrational behavior, these market conditions will likely persist until long after the economy recovers. Ben Marks And Brett Angel, Star Tribune, "The Fed helped revive stocks, but its actions created new risks," 12 Sep. 2020 Recent Examples on the Web: Noun 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

13 Oct 2020

Cite this Entry

“Irrational.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/irrational. Accessed 22 Oct. 2020.

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More Definitions for irrational

irrational

adjective
How to pronounce irrational (audio)

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

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