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irrational

play
adjective ir·ra·tio·nal \i-ˈra-sh(ə-)nəl, ˌi(r)-\

Definition of irrational

  1. :  not rational: such asa (1) :  not endowed with reason or understanding (2) :  lacking usual or normal mental clarity or coherenceb :  not governed by or according to reason irrational fearsc Greek & Latin prosody (1) of a syllable :  having a quantity other than that required by the meter (2) of a foot :  containing such a syllabled (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

irrationality

play \i-ˌra-shə-ˈna-lə-tē, ˌi(r)-\ noun

irrationally

play \i-ˈra-sh(ə-)nə-lē, ˌi(r)-\ adverb

See irrational defined for English-language learners

See irrational defined for kids

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Examples of irrational in a Sentence

  1. He became irrational as the fever got worse.

  2. She had an irrational fear of cats.

Origin and Etymology of irrational

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

irrational Synonyms

Synonyms
fallacious, illegitimate, inconsequent, inconsequential, invalid, illogical, nonrational, unreasonable, unreasoning, unsound, weak
Antonyms
logical, rational, reasonable, sound, valid, well-founded, well-grounded
Related Words
eristic (also eristical), misleading, sophistic (or sophistical), specious; half-baked, ill-advised, misguided, unconsidered, unreasoned; inconsistent; absurd, asinine, foolish, meaningless, nonsensical, preposterous, reasonless, senseless, silly; Kafkaesque, odd, peculiar, strange, surreal, unusual, weird; insane, mad, nutty, wacky (also whacky); disordered, disorganized, rambling, random; unconvincing; inexplicable, unaccountable, unexplainable
Near Antonyms
commonsense, sane, sensible, sober, wise; enlightened, informed, just, justified, reasoned; ordered, organized; clear, cogent, compelling, convincing, credible, persuasive, plausible, satisfying, solid; certain, sure, true; confirmed, corroborated, demonstrated, established, substantiated, validated
2

irrational

noun ir·ra·tio·nal

Definition of irrational

  1. 1 :  an irrational being

  2. 2 :  irrational number

First Known Use of irrational

1646

IRRATIONAL Defined for English Language Learners

irrational

play
adjective

Definition of irrational for English Language Learners

  • : not thinking clearly : not able to use reason or good judgment

  • : not based on reason, good judgment, or clear thinking

IRRATIONAL Defined for Kids

irrational

play
adjective ir·ra·tio·nal \i-ˈra-shə-nəl\

Definition of irrational for Students

  1. 1 :  not able to reason The fever made him irrational.

  2. 2 :  not based on reason irrational fears

irrationally

adverb

Medical Dictionary

irrational

play
adjective ir·ra·tio·nal \(ˈ)ir-ˈ(r)ash-nəl, -ən-əl\

Medical Definition of irrational

  1. :  not rational: asa:  lacking usual or normal mental clarity or coherence was irrational for several days after the accidentb:  not governed by or according to reason irrational fears

irrationality

\(ˌ)ir-ˌ(r)ash-ə-ˈnal-ət-ē\play noun plural

irrationalities

irrationally

\(ˈ)ir-ˈ(r)ash-nə-lē, -ən-əl-ē\play adverb

Law Dictionary

irrational

play
adjective ir·ra·tio·nal \ir-ˈra-shə-nəl\

Legal Definition of irrational

  1. :  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

irrationality

\ir-ˌra-shə-ˈna-lə-tē\ play noun

irrationally

adverb

Learn More about irrational

  1. Thesaurus: All synonyms and antonyms for irrational Spanish Central: Translation of irrational Nglish: Translation of irrational for Spanish speakers Britannica English: Translation of irrational for Arabic speakers

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Examples: irrational in a Sentence