Webster's Revised Unabridged Dictionary · 1913

Rational

Rational (rash"un*al) , adjective

[Latin rationalis: compare French rationnel. See Ratio, Reason, and compare Rationale.]

1.
Relating to the 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 under Formula.
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
Collocations (3)
Rational horizon (Astronomy) , See Horizon, 2 (b).
Rational quantity (Algebra) , one that can be expressed without the use of a radical sign, or in exact parts of unity; -- opposed to irrational or radical quantity.
Rational symptom (Medicine) , one elicited by the statements of the patient himself and not as the result of a physical examination.

Rational , noun

A rational being. — Young