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) : not endowed with reason or understanding
(2) : lacking usual or normal mental clarity or coherence
b : not governed by or according to reason irrational fears

c Greek & 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

To those of us who would like our language to be a bit more concise than a dog’s bark, a phobia is an irrational fear. James Lileks, National Review, "Girth Dearth," 11 July 2019 Overactive imaginations can be dangerously irrational while also being the hallmark of great storytellers everywhere. Sophie Gilbert, The Atlantic, "The American Paranoia of Stranger Things 3," 4 July 2019 So there is a bit of irrational exuberance whenever some youngster comes along with the sort of skill and poise Auger-Aliassime seems to possess. Howard Fendrich, SFChronicle.com, "Just 18, Canada’s ‘FAA’ taking flight in Wimbledon’s men’s draw," 3 July 2019 In the hanging-chad 2000 election, George W. Bush paid no discernible political price for his party’s irrational exuberance in impeaching Clinton. Walter Shapiro, The New Republic, "1998 Was a Seinfeld Election—Not an Impeachment Referendum," 6 June 2019 His exploration begins with pi, the irrational mathematical constant 3.14159, plus some, ad infinitum. Ephrat Livni, Quartz, "Two new books will transform your everyday understanding of math," 17 June 2019 Chandler encouraged community members to stay informed and avoid irrational conclusions. Max Londberg, Cincinnati.com, "Health official: Planned study will review cancer rates near Portsmouth uranium plant," 5 June 2019 Somehow, or perhaps inevitably, the attention of those on the right found its way to their latest favorite target of irrational hatred and persecution, Representative Ilhan Omar. Dennis Tang, Teen Vogue, "Trump's Offer to Help Notre-Dame Rebuild Doesn't Match His Response to Puerto Rico's Disaster," 19 Apr. 2019 The level of methamphetamine in Keel’s blood did not approach the amount seen in drug abusers who exhibit violent and irrational behavior, according to the medical examiner’s findings. Zak Koeske, Daily Southtown, "Son of Harvey cop shot security guards, patron before being killed, sheriff's investigation finds," 14 June 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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Statistics for irrational

Last Updated

16 Jul 2019

Look-up Popularity

Time Traveler for irrational

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

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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 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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Comments on irrational

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