[ra.tio.nal] adj [ME racional, fr. L rationalis, fr. ration-, ratio] (14c) 1 a: having reason or understanding b: relating to, based on, or agreeable to reason: reasonable "a ~ explanation" "~ behavior"
2: involving only multiplication, division, addition, and subtraction and only a finite number of times
3: relating to, consisting of, or being one or more rational numbers "a ~ root of an equation" -- ra.tio.nal.ly adv -- ra.tio.nal.ness n
[2]rational n (1606): something rational; specif: rational number