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[rash-uh-nl, rash-nl] /ˈræʃ ə nl, ˈræʃ nl/
agreeable to reason; reasonable; sensible:
a rational plan for economic development.
having or exercising reason, sound judgment, or good sense:
a calm and rational negotiator.
being in or characterized by full possession of one's reason; sane; lucid:
The patient appeared perfectly rational.
endowed with the faculty of reason:
rational beings.
of, relating to, or constituting reasoning powers:
the rational faculty.
proceeding or derived from reason or based on reasoning:
a rational explanation.
  1. capable of being expressed exactly by a ratio of two integers.
  2. (of a function) capable of being expressed exactly by a ratio of two polynomials.
Classical Prosody. capable of measurement in terms of the metrical unit or mora.
Mathematics. rational number.
Origin of rational
1350-1400; Middle English racional < Latin ratiōnālis, equivalent to ratiōn- (stem of ratiō) reason + -ālis -al1
Related forms
rationally, adverb
rationalness, noun
antirational, adjective
antirationally, adverb
hyperrational, adjective
hyperrationally, adverb
nonrational, adjective
nonrationally, adverb
overrational, adjective
overrationally, adverb
prerational, adjective
quasi-rational, adjective
quasi-rationally, adverb
transrational, adjective
transrationally, adverb
ultrarational, adjective
ultrarationally, adverb
unrational, adjective
unrationally, adverb
Can be confused
rational, reasonable (see synonym study at reasonable)
2. intelligent, wise, judicious, sagacious, enlightened. 6. See reasonable.
2. stupid. 3. insane. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the Web for rational
Contemporary Examples
Historical Examples
  • Though he had no rational reason for expecting trouble he had still his hunch and his intuition.

    The Blind Spot Austin Hall
  • Shall he alone, whom rational we call, Be pleased with nothing, if not blessed with all?

    Essay on Man Alexander Pope
  • We are experiencing in the world-war a fearful balancing-up with the rational intentionality of organised culture.

  • Enacted institutions are products of rational invention and intention.

    Folkways William Graham Sumner
  • The natural turn of his temper inclined him to rational society, but in that his wife could bear no part.

British Dictionary definitions for rational


using reason or logic in thinking out a problem
in accordance with the principles of logic or reason; reasonable
of sound mind; sane: the patient seemed quite rational
endowed with the capacity to reason; capable of logical thought: man is a rational being
(maths) expressible as a ratio of two integers or polynomials: a rational number; a rational function
(maths) a rational number
Derived Forms
rationally, adverb
rationalness, noun
Word Origin
C14: from Latin ratiōnālis, from ratiōreason
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
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Word Origin and History for rational

late 14c., "pertaining to reason;" mid-15c., "endowed with reason," from Old French racionel and directly from Latin rationalis "of or belonging to reason, reasonable," from ratio (genitive rationis) "reckoning, calculation, reason" (see ratio).

Online Etymology Dictionary, © 2010 Douglas Harper
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rational in Medicine

rational ra·tion·al (rāsh'ə-nəl)

  1. Having or exercising the ability to reason.

  2. Influenced by reasoning rather than by emotion.

  3. Of sound mind; sane.

  4. Based on scientific knowledge or theory rather than practical observation.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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rational in Technology

[Mathematics] a fractional number n/d, where n and d are integers, n is the numerator and d is the denominator. The set of all rational numbers is usually called Q. Computers do not usually deal with rational numbers but instead convert them to real numbers which are represented (approximately in some cases) as floating-point numbers. Compare irrational.

The Free On-line Dictionary of Computing, © Denis Howe 2010
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