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 number
Examples of rational in a Sentence
Adjective
human beings are rational creatures
insisted there was a rational explanation for the strange creaking noises and that there were no such things as ghosts
Recent Examples on the Web
Roya Hakakian, The Atlantic, 10 July 2025
A lot of court cases have been dealing with these cancellations as a group, highlighting the lack of scientific—or seemingly rational—input into the decisions to cut funding for entire categories of research.
—ArsTechnica, 9 July 2025
Jordana Cepelewicz, Quanta Magazine, 21 June 2024
At the time the database had a little over 3 million elliptic curves over the rationals.
—Lyndie Chiou, Quanta Magazine, 5 Mar. 2024
See All Example Sentences for rational
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Adjective
The regime’s more rational elements may eventually prevail and reduce tensions.
—Roya Hakakian, The Atlantic, 10 July 2025
A lot of court cases have been dealing with these cancellations as a group, highlighting the lack of scientific—or seemingly rational—input into the decisions to cut funding for entire categories of research.
—ArsTechnica, 9 July 2025
Noun
For instance, in one group, collect all rationals that, when squared, are less than 2; in the other, put all rationals whose squares are greater than 2.
—Jordana Cepelewicz, Quanta Magazine, 21 June 2024
At the time the database had a little over 3 million elliptic curves over the rationals.
—Lyndie Chiou, Quanta Magazine, 5 Mar. 2024
See All Example Sentences for rational
Cite this Entry
“Rational.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/rational. Accessed 22 Jul. 2025.
Copy CitationKids Definition
rational
1 of 2 adjective
ra·tio·nal
ˈrash-nəl 
-ən-ᵊl
1
a
: having the ability to reason
rational beings
b
: relating to, based on, or showing reason : reasonable sense 2
rational behavior
2
: relating to or involving rational numbers
a rational fraction
rationally
adverb
-ē
rational
2 of 2 noun
: something rational
especially
: rational number
Medical Definition
rational
adjective
ra·tio·nal
ˈrash-nəl, -ən-ᵊl
1
a
: having reason or understanding
b
: relating to, based on, or agreeable to reason
a rational explanation
rational behavior
2
: using medical treatments based on reason or general principles
—used especially of an ancient school of physicians
compare empirical sense 1a
Legal Definition
rational
adjective
ra·tio·nal
ˈra-shə-nəl
1
: having reason or understanding
2
: relating to, based on, or guided by reason, principle, fairness, logic, a legitimate state interest, or a consideration of fact
age distinctions are not subject to strict scrutiny, but they must have a rational relationship to a legitimate state interest—In re J. M., 642 A.2d 1062 (1994)
In re J. M., 642 A.2d 1062 (1994)
rationally
adverb
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