- without the faculty of reason; deprived of reason.
- without or deprived of normal mental clarity or sound judgment.
- not in accordance with reason; utterly illogical: irrational arguments.
- not endowed with the faculty of reason: irrational animals.
- (of a number) not capable of being expressed exactly as a ratio of two integers.
- (of a function) not capable of being expressed exactly as a ratio of two polynomials.
- Algebra. (of an equation) having an unknown under a radical sign or, alternately, with a fractional exponent.
- Greek and Latin Prosody.
- of or relating to a substitution in the normal metrical pattern, especially a long syllable for a short one.
- noting a foot or meter containing such a substitution.
- Mathematics. irrational number.
Origin of irrational
SynonymsSee more synonyms on Thesaurus.com
Examples from the Web for irrational
The fact that the virus is still alive has sustained many safety concerns, both rational and irrational, about its use.Powdered Measles Vaccine Could Be Huge for Developing World
December 2, 2014
To a certain degree, there is an irrational sense of betrayal.Renee Zellweger's Face Gets More Medical Scrutiny Than Ebola
October 21, 2014
But with no sign of an epidemic in the U.S. it seems, at the very least, irrational.Ebola Panic Is Worse Than the Disease
October 9, 2014
One of the reasons the Vikings are viewed so negatively is that their violence could seem wanton or irrational.How the Vikings Saved Europe and Got a Terrible Reputation
September 17, 2014
I must confess to a fugitive and irrational wish that he might find some small mercies there.Tupac and Murray Kempton: The Godfather Who Wore Tweed
June 22, 2014
I haven't been irrational, I give you my word, not once since I came here.The Spenders
Harry Leon Wilson
This reply seemed to arouse an irrational anger in the Briton.The Cruise of the Dry Dock
T. S. Stribling
If men cannot have a rational belief, they will have an irrational.Laws
Pride was irrational, and so was the greater part of human misery.Mezzerow Loves Company
Floyd L. Wallace
In spite of his fine manner and bearing, his every word had been irrational.Elsie Marley, Honey
- inconsistent with reason or logic; illogical; absurd
- incapable of reasoning
- not rational
- (as noun)an irrational
- prosody (in Greek or Latin verse)
- of or relating to a metrical irregularity, usually the occurrence of a long syllable instead of a short one
- denoting a metrical foot where such an irregularity occurs
Word Origin and History for irrational
late 15c., "not endowed with reason" (of beats, etc.); earlier (of quantities) "inexpressible in ordinary numbers" (late 14c.); from Latin irrationalis "without reason," from assimilated form of in- "not, opposite of" (see in- (1)) + rationalis "reason" (see rational). Meaning "illogical, absurd" is attested from 1640s. Related: Irrationally.
- Not rational; marked by a lack of accord with reason or sound judgment.