rational

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Having or exercising the ability to reason.
2. adj. Of sound mind; sane.
3. adj. Consistent with or based on reason; logical: rational behavior. See Synonyms at logical.
4. adj. Mathematics Capable of being expressed as a quotient of integers.
5. n. Mathematics A rational number.

Century Dictionary and Cyclopedia

1. Of, pertaining to, or springing from the reason, in the sense of the highest faculty of cognition.
2. Endowed with reason, in the sense of that faculty which distinguishes man from the brutes: as, man is a rational animal.
3. Conformable to the precepts of reason, especially of the practical reason; reasonable; wise.
4. In arithmetic and algebra:
5. Expressible in finite terms: applied to expressions in which no extraction of a root is left, or, at least, none such indicated which cannot be actually performed by known processes. The contraries of these are called surd or irrational quantities. Thus 2, 12½, 9, are rational quantities, and etc., are irrational or surd quantities, because their values can only be approximately and not accurately assigned.
6. In Euclid's “Elements” and commentaries, etc., on that work, commensurable with a given line. In senses
7. In ancient prosody, capable of measurement in terms of the metrical unit (semeion or mora). A rational time (χρόνος ρ)ητός) is a time divisible by this unit without remainder. Thus, disemic times (times of two semeia) are rational, while irrational times (χρόνοι α+λογοι) can be expressed only by fractions (as ¾, 1½, 2½, 2⅔) of a semeion.
8. The composition of elements which only differ as viewed by the mind, and not as they exist, as the composition of essence and existence, of being and relation, etc.
9. The union of several objects so far as they are brought together into or under one concept.
10. The limits of rational knowledge.
11. Knowledge springing directly or indirectly from reason, and not from experience.
12. Synonyms Rational, Reasonable, sensible, enlightened, discreet, intelligent, sane, sound. The first two words are somewhat different, according as they refer to persons or things. As to persons, rational is the more speculative, reasonable the more practical term; rational means possessing the faculty of reason, while reasonable means exercising reason in its broader sense, in opposition to unreasonable—that is, guided by prejudice, fancy, etc. In fever the patient may become irrational and give irrational answers; when he is rational he may through weakness and fretfulness make unreasonable demands of his physician. As to things, the distinction continues between the narrower and the broader senses: a rational proposition is one that might proceed from a rational mind; a reasonable proposition is one that is marked by common sense and fairness. It is irrational to look for a coal-mine in a granite-ledge; it is unreasonable to expect good work for poor pay. See absurd.
13. n. A quiddity; a universal; a. nature. Thus, in the first quotation “the world of rationals” is the rational world, the system of general or possible entities. The conception is Platonic.
14. n. Eccles.:
15. n. The breastplate of the Jewish high-priest. The name rational for the Jewish high-priest's breastplate (Hebrew chōshen, an ‘ornament,’ according to others a ‘pouch’ or ‘receptacle’) comes from the Latin rationale, a mistaken translation in the Vulgate of the word λόγιον or λογεϊον in the Septuagint, etc., meaning an ‘oracle’ or ‘oracular instrument,’ with allusion to the consultation of the Urim and Thummim.
16. n. Hence— A square plate of gold, silver, or embroidery, either jeweled or enameled, formerly worn on the breast over the chasuble by bishops during the celebration of mass. Also pectoral and rationale in both senses.
17. n. In mathematics, a rational number.
18. n. One who is a believer in so-called ‘rational’ reforms, as in dress or food.

Wiktionary

1. adj. Capable of reasoning.
2. adj. Logically sound; not contradictory or otherwise absurd.
3. adj. Healthy or balanced intellectually; exhibiting reasonableness.
4. adj. mathematics, arithmetic, number theory, not comparable Of a number, capable of being expressed as the ratio of two integers.
5. adj. mathematics, arithmetic, not comparable Of an algebraic expression, capable of being expressed as the ratio of two polynomials.
6. n. mathematics A rational number: a number that can be expressed as the quotient of two integers.
7. n. A rational being.

GNU Webster's 1913

1. adj. Relating to the reason; not physical; mental.
2. adj. Having reason, or the faculty of reasoning; endowed with reason or understanding; reasoning.
3. adj. Agreeable to reason; not absurd, preposterous, extravagant, foolish, fanciful, or the like; wise; judicious.
4. adj. (Chem.) Expressing the type, structure, relations, and reactions of a compound; graphic; -- said of formulæ. See under Formula.
5. n. A rational being.

WordNet 3.0

1. n. an integer or a fraction
2. adj. having its source in or being guided by the intellect (as distinguished from experience or emotion)
3. adj. of or associated with or requiring the use of the mind
4. adj. capable of being expressed as a quotient of integers
5. adj. consistent with or based on or using reason