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See more synonyms for irrationality on Thesaurus.com
noun, plural ir·ra·tion·al·i·ties for 2.
  1. the quality or condition of being irrational.
  2. an irrational, illogical, or absurd action, thought, etc.
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Origin of irrationality

First recorded in 1560–70; irrational + -ity
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words

foolishness, impracticality, illogicality, insanity, unreasonableness

Examples from the Web for irrationality

Contemporary Examples

Historical Examples

  • But machines could not hope to encompass all the irrationality of Man.

    Mezzerow Loves Company

    Floyd L. Wallace

  • Elsmere's irrationality was an aversion to doctors, from the point of view of his own ailments.

    Robert Elsmere

    Mrs. Humphry Ward

  • This is the fourth example of irrationality, or incommensurability.

  • This is the fifth example of irrationality and incommensurability.

  • The irrationality of the defence was a final proof that the lawyer had played him false.

    Gulmore, The Boss

    Frank Harris

British Dictionary definitions for irrationality



  1. the state or quality of being irrational
  2. irrational thought, action, or behaviour
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for irrationality


1560s, from irrational + -ity.

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Online Etymology Dictionary, © 2010 Douglas Harper