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

rationally
adverb

rationalness
noun

**:**something rational

specifically

**:**rational numberLove words? Need even more definitions?

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Merriam-Webster unabridged
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