Definition of “rational” - English Dictionary

“rational” in British English

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rationaladjective

uk /ˈræʃ.ən.əl/ us /ˈræʃ.ən.əl/

C1 based on clear thought and reason:

There must be some rational explanation for what happened.
a rational act/course of action
a rational argument/decision
He was too upset to be rational.

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rationality
noun [ U ] uk /ˌræʃ.ənˈæl.ə.ti/ us /ˌræʃ.ənˈæl.ə.t̬i/

Science rests on the ideals of objectivity and rationality.

(Definition of “rational” from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

“rational” in American English

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rationaladjective

us /ˈræʃ·ə·nəl/

showing clear thought or reason:

a rational decision
Obviously, he wasn’t rational.
rationally
adverb [ not gradable ] us /ˈræʃ·ə·nəl·i/

It’s hard to behave rationally at such times.

(Definition of “rational” from the Cambridge Academic Content Dictionary © Cambridge University Press)