irrational

/iˈræʃɪnəl/

/ɪˈræʃənəl/

Other forms: irrationals

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.

Definitions of irrational

1. adjective

   not consistent with or using reason
   “irrational fears”

   “irrational animals”

   synonyms:

   incoherent

   without logical or meaningful connection

   illogical, unlogical

   lacking in correct logical relation

   blind, unreasoning

   not based on reason or evidence

   reasonless

   not endowed with the capacity to reason

   nonrational

   not based on reason

   superstitious

   showing ignorance of the laws of nature and faith in magic or chance

   unreasonable

   not reasonable; not showing good judgment

   antonyms:

   rational

   consistent with or based on or using reason

   logical

   capable of or reflecting the capability for correct and valid reasoning

   coherent, logical, lucid

   capable of thinking and expressing yourself in a clear and consistent manner

   demythologised, demythologized

   having mythical elements removed

   intelligent, reasoning, thinking

   endowed with the capacity to reason

   reasonable, sane

   marked by sound judgment

   reasonable, sensible

   showing reason or sound judgment

   sane

   mentally healthy; free from mental disorder
2. adjective

   real but not expressible as the quotient of two integers
   “irrational numbers”

   antonyms:

   rational

   capable of being expressed as a quotient of integers
3. noun

   a real number that cannot be expressed as a rational number
   synonyms: irrational number

   types:

   transcendental number

   an irrational number that is not algebraic

   algebraic number

   root of an algebraic equation with rational coefficients

   pi

   the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846...

   e

   the base of the natural system of logarithms; approximately equal to 2.718282...

   type of:

   real, real number

   any rational or irrational number