irrational

American  

[ih-rash-uh-nl, -rash-nl] / ɪˈræʃ ə nl, -ˈræʃ 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 British  

/ 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

Etymology

Origin of irrational

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

Explanation

If you're a straight-A student and still you worry about failing all of your classes, you're being irrational. Your fears are not based on fact and not likely to come true. Usually you use irrational to describe ideas and thoughts that are not based on reason, although emotions and behavior can be irrational too if they don't seem reasonable. Do you jump onto a chair and scream when you see a mouse? If so, you have an irrational fear of mice, or musophobia. If someone takes a swing at you for failing to say excuse me when you burp, both their anger and their actions could be called irrational.

Example Sentences

So successful was he at it that NBC recently turned one of his books into a whole TV show, a detective thriller called The Irrational whose main character is loosely based on Ariely himself.

From Slate • Oct. 23, 2023

Irrational numbers include, for example, the square root of 2, whose decimal representation is infinite without ever repeating.

From Scientific American • May 23, 2023

It is based not just on extreme authority and emotionalism, but a cultivation and worship of the Irrational.

From Salon • Apr. 20, 2023

It began with the acquisition of his last company, Irrational Games, and continued with the dissolution of that studio and the creation of Ghost Story, which Take-Two also owns.

From Seattle Times • Jan. 10, 2022

For instance, I am significantly clear as to the price of the paper on which I wrote The Irrational Knot.

From The Irrational Knot Being the Second Novel of His Nonage by Shaw, Bernard

Related Words

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