I. ˈrash-nəl, ˈra-shə-n ə l adjective
Etymology: Middle English racional, from Anglo-French racionel, from Latin rationalis, from ration-, ratio
Date: 14th century
1.
a. : having reason or understanding
b. : relating to, based on, or agreeable to reason : reasonable
a rational explanation
rational 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 rational root of an equation
• ra·tio·nal·ly adverb
• ra·tio·nal·ness noun
II. noun
Date: 1606
: something rational ; specifically : rational number