Dictionary

1irrational

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

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

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

Full Definition of IRRATIONAL

:  not rational: 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>
ir·ra·tio·nal·i·ty \-ˌra-shə-ˈna-lə-tē\ noun
ir·ra·tio·nal·ly \-ˈra-sh(ə-)nə-lē\ adverb

Examples of IRRATIONAL

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

Origin of IRRATIONAL

Middle English, from Latin irrationalis, from in- + rationalis rational
First Known Use: 14th century

2irrational

noun

Definition of IRRATIONAL

1
:  an irrational being

First Known Use of IRRATIONAL

1646

Rhymes with IRRATIONAL

IRRATIONALLY Defined for Kids

irrational

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

Definition of IRRATIONAL for Kids

1
:  not able to reason <The fever made him irrational.>
2
:  not based on reason <irrational fears>
ir·ra·tio·nal·ly adverb
Medical Dictionary

irrational

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

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>
ir·ra·tio·nal·i·ty \(ˌ)ir-ˌ(r)ash-ə-ˈnal-ət-ē\ noun, plural ir·ra·tio·nal·i·ties
ir·ra·tio·nal·ly \(ˈ)ir-ˈ(r)ash-nə-lē, -ən-əl-ē\ adverb

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