- of, based on, or derived from reasoning:
*rational*powers - able to reason; reasoning; in possession of one's reason or sanity
- showing reason; not foolish or silly; sensible: a
*rational*argument - Math.
- designating or of a real number or quantity expressible as the ratio of two integers, with the second integer not being equal to zero: all integers and fractions are rational numbers
- designating a function expressible as the quotient of two polynomials

Origin of rational

Middle English*racional*from Classical Latin

*rationalis*from

*ratio*: see reason