rational

1 of 2

adjective

ra·​tio·​nal ˈrash-nəl 

ˈra-shə-nᵊl

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

rational

2 of 2

noun

: something rational

specifically : rational number

Synonyms

Adjective

• intelligent
• reasonable
• reasoning
• thinking

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

Adjective

President Donald Trump’s court challenge failed during his first term because his administration did not provide the U.S. Supreme Court with a rational government basis for terminating the program. —Darren Soto, The Orlando Sentinel, 22 June 2025

The court's majority found that Tennessee's law is not subject to a heightened level of judicial review and satisfies the most deferential standard, known as rational basis. —June 18, CBS News, 18 June 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

Word History

Etymology

Adjective

Middle English racional, from Anglo-French racionel, from Latin rationalis, from ration-, ratio

First Known Use

Adjective

14th century, in the meaning defined at sense 1a

Noun

1601, in the meaning defined above

Phrases Containing rational

• anti-rational
• hyper-rational
• rational function
• rational number
• sub-rational

Rhymes for rational

• national
• binational
• irrational
• subnational
• transnational
• international
• multinational
• supranational

Kids 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

-ē

adverb

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

rationally

-ē 

adverb

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)

rationality

ˌra-shə-ˈna-lə-tē 

noun

rationally adverb