irrational

[ih-rash-uh-nl, -rash-nl]

adjective

1. without the faculty of reason; deprived of reason.

2. without or deprived of normal mental clarity or sound judgment.

3. not in accordance with reason; utterly illogical.

   irrational arguments.

   Synonyms: insensate, ridiculous, unreasonable

4. not endowed with the faculty of reason.

   irrational animals.

5. Mathematics.

   1. (of a number) not capable of being expressed exactly as a ratio of two integers.

   2. (of a function) not capable of being expressed exactly as a ratio of two polynomials.

6. Algebra.,  (of an equation) having an unknown under a radical sign or, alternately, with a fractional exponent.

7. Greek and Latin Prosody.

   1. of or relating to a substitution in the normal metrical pattern, especially a long syllable for a short one.

   2. noting a foot or meter containing such a substitution.

noun

1. Mathematics.,  irrational number.

irrational

/ ɪˈræʃənəl /

adjective

1. inconsistent with reason or logic; illogical; absurd

2. incapable of reasoning

3. maths

   1. not rational

   2. ( as noun )

      an irrational

4. prosody

   1. of or relating to a metrical irregularity, usually the occurrence of a long syllable instead of a short one

   2. denoting a metrical foot where such an irregularity occurs

Other Word Forms

• irrationally adverb
• irrationalness noun
• nonirrational adjective
• nonirrationalness noun

Word History and Origins

Origin of irrational¹

First recorded in 1425–75; late Middle English, from Latin irratiōnālis; ir- ² ( def. ), rational ( def. )

Example Sentences

Gavekal Research suggests the current AI investment climate resembles an “irrational bubble” due to high marginal costs and capital intensity.

Read more on Barron's

She told a conference of police leaders "the structure of our police forces is, if we are honest, irrational".

Read more on BBC

“The market can remain irrational longer than you can remain solvent,” is a financial industry shibboleth most investors have learned through a great deal of pain.

Read more on Barron's

Exxon Mobil has taken issue with those reporting rules too: Chief Executive Darren Woods has described the rules in Europe—known as the Corporate Sustainability Due Diligence Directive—as “an irrational piece of policy.”

Read more on The Wall Street Journal

At the same time, the bears argue that it’s a sign of potentially irrational exuberance when margin debt increases for many months in a row.

Read more on MarketWatch

Related Words

• aberrant 
• absurd 
• crazy 
• foolish 
• incoherent 
• insane 
• preposterous 
• ridiculous 
• stupid 
• unreasonable 
• unsound 
• unwise 
• wrong