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rational

[rash-uh-nl, rash-nl]
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adjective
  1. agreeable to reason; reasonable; sensible: a rational plan for economic development.
  2. having or exercising reason, sound judgment, or good sense: a calm and rational negotiator.
  3. being in or characterized by full possession of one's reason; sane; lucid: The patient appeared perfectly rational.
  4. endowed with the faculty of reason: rational beings.
  5. of, relating to, or constituting reasoning powers: the rational faculty.
  6. proceeding or derived from reason or based on reasoning: a rational explanation.
  7. Mathematics.
    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.
  8. Classical Prosody. capable of measurement in terms of the metrical unit or mora.
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noun
  1. Mathematics. rational number.
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Origin of rational

1350–1400; Middle English racional < Latin ratiōnālis, equivalent to ratiōn- (stem of ratiō) reason + -ālis -al1
Related formsra·tion·al·ly, adverbra·tion·al·ness, nounan·ti·ra·tion·al, adjectivean·ti·ra·tion·al·ly, adverbhy·per·ra·tion·al, adjectivehy·per·ra·tion·al·ly, adverbnon·ra·tion·al, adjectivenon·ra·tion·al·ly, adverbo·ver·ra·tion·al, adjectiveo·ver·ra·tion·al·ly, adverbpre·ra·tion·al, adjectivequa·si-ra·tion·al, adjectivequa·si-ra·tion·al·ly, adverbtrans·ra·tion·al, adjectivetrans·ra·tion·al·ly, adverbul·tra·ra·tion·al, adjectiveul·tra·ra·tion·al·ly, adverbun·ra·tion·al, adjectiveun·ra·tion·al·ly, adverb
Can be confusedrational reasonable (see synonym study at reasonable)

Synonyms

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2. intelligent, wise, judicious, sagacious, enlightened. 6. See reasonable.

Antonyms

2. stupid. 3. insane.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for rational

rational

adjective
  1. using reason or logic in thinking out a problem
  2. in accordance with the principles of logic or reason; reasonable
  3. of sound mind; sanethe patient seemed quite rational
  4. endowed with the capacity to reason; capable of logical thoughtman is a rational being
  5. maths expressible as a ratio of two integers or polynomialsa rational number; a rational function
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noun
  1. maths a rational number
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Derived Formsrationally, adverbrationalness, noun

Word Origin

C14: from Latin ratiōnālis, from ratiō reason
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 rational

adj.

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).

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Online Etymology Dictionary, © 2010 Douglas Harper

rational in Medicine

rational

(răshə-nəl)
adj.
  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.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.