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

• irrationalness noun
• irrationally adverb
• 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

But you don’t have to look far to see its inverse — people being irrational, superstitious, fearful, cruel.

From Los Angeles Times

“My absolute belief that I could not get away. Maybe it sounds completely irrational and unreasonable today.”

From Los Angeles Times

Liberty Steel said the decision to put the firm into compulsory liquidation was "irrational".

From BBC

Her lawyers at the firm Leigh Day argue the decision is "irrational".

From BBC

Men are born to be strong, domineering and intelligent, while women are fated to be weak, submissive and emotionally irrational.

From Salon

Related Words

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