irrational

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

Definition of irrational

: 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

Examples of irrational in a Sentence

He became irrational as the fever got worse.
She had an irrational fear of cats.

Origin and Etymology of irrational

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

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First Known Use: 14th century

See Words from the same year

irrational

noun ir·ra·tio·nal

Definition of irrational

1 : an irrational being
2 : irrational number

First Known Use of irrational

1646

IRRATIONAL Defined for English Language Learners

irrational

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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-n^əl\

Definition of irrational for Students

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

: 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

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

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