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

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 Male presidential candidates are noted for their inexplicable and sudden desires to do irrational things, such as assassinate Alexander Hamilton, create the Bull Moose Party or be John Edwards. Alexandra Petri, Twin Cities, "Alexandra Petri: Can we risk nominating a man for president?," 13 June 2019 Kevin Durant’s decision to play through his calf injury was emotional, irrational and flat-out foolish. Greg Moore, azcentral, "Kevin Durant playing through injury shows love for game — it's why Toronto fans ended up cheering," 10 June 2019 Activists, philosophers, and politicians are increasingly beginning to make this very claim about climate change: that inaction is not only irrational, a profound threat to our own sense of self-preservation, but immoral. Nathaniel Rich, Harper's magazine, "Ruina Mundi," 10 May 2019 Trump’s behavior toward Sessions appears erratic and irrational. Jonathan Chait, Daily Intelligencer, "How Trump Could Get Scott Pruitt to Fire Robert Mueller," 11 June 2018 Remember when there were a few dim beams of (irrational) hope that Ivanka Trump could be some sort of secret resistance warrior in the Trump White House? Michelle Ruiz, Vogue, "Meanwhile, in China, Ivanka Trump’s Business Doesn’t Seem So Defunct After All," 22 Jan. 2019 Agents can be rational or irrational, greedy or fearful, and have all sorts of restrictions and motivations. Paul J. Davies, WSJ, "A New Way to Spot the Next Financial Crisis," 18 Dec. 2018 Image Strong women in China are often portrayed as power-hungry, and sometimes irrational, and are notably absent from the highest ranks of government. New York Times, "Was This Powerful Chinese Empress a Feminist Trailblazer?," 10 July 2018

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

18 Jun 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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