The Collaborative International Dictionary of English v.0.48:
Rational \Ra"tion*al\ (r[a^]sh"[u^]n*al), a. [L. rationalis: cf.
F. rationnel. See Ratio, Reason, and cf. 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.
2. Having reason, or the faculty of reasoning; endowed with
reason or understanding; reasoning.
It is our glory and happiness to have a rational
3. Agreeable to reason; not absurd, preposterous,
extravagant, foolish, fanciful, or the like; wise;
judicious; as, rational conduct; a rational man.
4. (Chem.) Expressing the type, structure, relations, and
reactions of a compound; graphic; -- said of formulae. See
Rational horizon. (Astron.) See Horizon, 2
Rational quantity (Alg.), 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 (Med.), one elicited by the statements of
the patient himself and not as the result of a physical
Syn: Sane; sound; intelligent; reasonable; sensible; wise;
Usage: Rational, reasonable. Rational has reference to
reason as a faculty of the mind, and is opposed to
irrational; 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 desires or plans; a
reasonable charge; a reasonable prospect of success.
What higher in her society thou find'st
Attractive, human, rational, love still.
A law may be reasonable in itself, although a
man does not allow it, or does not know the
reason of the lawgivers. --Swift.