[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.

(02 Feb 2009)

1. Relating to reason; not physical; mental. "Moral philosophy was his chiefest end; for the rational, the natural, and mathematics . . . Were but simple pastimes in comparison of the other." (Sir T. North)

2. Having reason, or the faculty of reasoning; endowed with reason or understanding; reasoning. "It is our glory and happiness to have a rational nature." (Law)

3. Agreeable to reason; not absurd, preposterous, extravagant, foolish, fanciful, or the like; wise; judicious; as, rational conduct; a rational man.

4. <chemistry> Expressing the type, structure, relations, and reactions of a compound; graphic; said of formulae. See Formula. Rational horizon.

<astronomy> See Horizon, 2 .

<mathematics> Rational quantity, one elicited by the statements of the patient himself and not as the result of a physical examination.

Synonyms: Sane, sound, intelligent, reasonable, sensible, wise, discreet, judicious.

Rational, reasonable. Rational has reference to reason as a faculty of the mind, and is opposed to traditional; as, a rational being, a rational state of mind, rational views, etc. In these cases the speculative reason is more particularly, referred to. Reasonable has reference to the exercise of this faculty for practical purposes, and means, governed or directed by reason; as, reasonable prospect of success. "What higher in her society thou find'st Attractive, human, rational, love still." (Milton) "A law may be reasonable in itself, although a man does not allow it, or does not know the reason of the lawgivers." (Swift)

Origin: L. Rationalis: cf. F. Rationnel. See Ratio, Reason, and cf. Rationale.

(01 Mar 1998)