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rational

adj. · n.
US //ˈɹæʃənəɫ// UK //ɹˈæʃənəl// ra·tio·nal
  1. 1 logical and sensible (adj.)
    B2 Upper Intermediate

    based on clear thinking and facts rather than emotions.

    based on or in accordance with reason or logic; exhibiting intellectual soundness.

    Example

    We need to have a rational discussion about the budget instead of getting angry.

    Example

    The committee attempted to reach a rational conclusion by weighing the statistical evidence against the projected long-term costs.
  2. 2 capable of reasoning (adj.)
    C1 Advanced Academic

    having the ability to think, understand, and use logic.

    possessing the capacity for reason; often used to distinguish humans from other animals in philosophical contexts.

    Example

    Aristotle famously described humans as rational animals.

    Example

    The debate centered on whether artificial intelligence could ever truly be considered a rational agent with its own intent.
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  1. 3 math/ratios (adj.)
    B2 Upper Intermediate Technical Math

    describing a number that can be shown as a simple fraction.

    relating to or being a number that can be expressed as the quotient of two integers.

    Example

    The number 0.75 is rational because it can be written as three-quarters.

    Example

    The proof demonstrates that while the square root of two is irrational, its square is a rational integer.
  2. 4 a rational number (n.)
    C1 Advanced Technical Math

    a number that can be expressed as one integer divided by another.

    a rational number; any value that can be represented as a ratio of two integers where the denominator is not zero.

    Example

    In this equation, x must be a rational rather than an irrational number.

    Example

    The set of rationals is dense, meaning that between any two distinct rational numbers, there exists another rational.
Etymology 1

From Old French rationel, rational, from Latin rationalis (“of or belonging to reason, rational, reasonable; having a ratio”), from ratio (“reason; calculation”).

Etymology 2

From Old French rational, from Medieval Latin rationale (“a pontifical stole, a pallium, an ornament worn over the chasuble”), neuter of Latin rationalis (“rational”), for which see the first etymology. Translation of λογεῖον (logeîon) or perhaps λόγιον (lógion, “oracle”) in the Septuagint version of Exodus 28.

Word family

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