Alternative formsEdit


  • enPR: ră'sh(ə)nəl, IPA(key): /ˈræʃ(ə)nəl/
  • (file)

Etymology 1Edit

From Old French rationel, rational, from Latin rationalis ‎(of or belonging to reason, rational, reasonable), from ratio ‎(reason)


rational ‎(comparative more rational, superlative most rational)

  1. Capable of reasoning.
    Man is a rational creature.
    • 2001, Mark Sainsbury, chapter 1, Logical Forms — An Introduction to Philosophical Logic, 2nd edition, Blackwell Publishing, ISBN 978-0-63121-679-7, §7, page 32:
      The utility of valid arguments is a monument to our frailty: to the fact that we are not completely rational beings.
  2. Logically sound; not contradictory or otherwise absurd.
    His statements were quite rational.
  3. (of a person or personal characteristics) Healthy or balanced intellectually; exhibiting reasonableness.
    rational conduct
    • 2014 June 21, “Magician’s brain”, The Economist, volume 411, number 8892: 
      The [Isaac] Newton that emerges from the [unpublished] manuscripts is far from the popular image of a rational practitioner of cold and pure reason. The architect of modern science was himself not very modern. He was obsessed with alchemy.
  4. (mathematics, arithmetic, number theory, not comparable) Of a number, capable of being expressed as the ratio of two integers.
    ¾ is a rational number, but √2 is an irrational number.
  5. (mathematics, arithmetic, not comparable) Of an algebraic expression, capable of being expressed as the ratio of two polynomials.
  6. (chemistry) Expressing the type, structure, relations, and reactions of a compound; graphic; said of formulae.
Related termsEdit


rational ‎(plural rationals)

  1. (mathematics) A rational number: a number that can be expressed as the quotient of two integers.
    The quotient of two rationals is again a rational.

Etymology 2Edit

From Old French rational, from Medieval Latin rationale ‎(a pontifical stole, a pallium, an ornament worn over the chasuble), neuter of Latin rationalis ‎(rational), for which see the first etymology. Translation of λογεῖον ‎(logeîon) or perhaps λόγιον ‎(lógion, oracle) in the Septuagint version of Exodus 28.


rational ‎(plural rationals)

  1. the breastplate worn by Israelite high priests
    1609, Douay-Rheims Bible, Exodus 28:15
    And thou shalt make the rational of judgment with embroidered work of divers colours, according to the workmanship of the ephod, of gold, violet, and purple, and scarlet twice dyed, and fine twisted linen.



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