First Known Use: 14th century
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
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Origin of IRRATIONAL
Middle English, from Latin irrationalis, from in- + rationalis rational
Related to IRRATIONAL
- Synonyms
- fallacious, illegitimate, inconsequent, inconsequential, invalid, illogical, nonrational, unreasonable, unreasoning, unsound, weak
- Antonyms
- logical, rational, reasonable, sound, valid, well-founded, well-grounded
2irrational
noun
Definition of IRRATIONAL
1
: an irrational being
First Known Use of IRRATIONAL
1646
Rhymes with IRRATIONAL
IRRATIONALITY 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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