1 of or based on reasoning or reason.
2 sensible, sane, moderate; not foolish or absurd or extreme.
3 endowed with reason, reasoning.
4 rejecting what is unreasonable or cannot be tested by reason in religion or custom.
5 Math. (of a quantity or ratio) expressible as a ratio of whole numbers.
Phrases and idioms:
rational dress hist. a style of dress adopted by some women in the late nineteenth century, including bloomers or knickerbockers. rational horizon see HORIZON 1c.
Derivatives:
rationality n. rationally adv.
Etymology: ME f. L rationalis (as RATION)
Useful english dictionary. 2012.