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dual

adj. · n. · v.
US //ˈduəɫ// UK //djˈuːəl// du·al
  1. 1 having two parts (adj.)
    B2 Upper Intermediate

    having two parts, or having two different purposes at the same time.

    consisting of two parts, elements, or aspects; often used to describe a single entity with two distinct functions.

    Example

    The new laptop has a dual purpose as both a computer and a tablet.

    Example

    The candidate holds dual citizenship, which complicates the security clearance process for the high-level government position.

    Usage

    Usually placed before the noun it modifies.
  2. 2 grammar (adj.)
    C1 Advanced Technical grammar

    a special form of a word used in some languages to talk about exactly two people or things.

    pertaining to a grammatical number that specifically denotes two of a kind, distinct from singular and plural.

    Example

    Some ancient languages have a dual form for pairs like eyes or hands.

    Example

    While Modern English relies on the plural, Old English utilised a dual number for the first and second person pronouns.

    Usage

    Used as a technical descriptor for morphological categories.
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  1. 3 mathematics/physics (adj.)
    C2 Proficiency Academic Technical Science

    describing a relationship where two things are opposites but also match each other perfectly.

    relating to duality, where one mathematical structure or physical theory can be translated into another.

    Example

    The scientist explained the dual nature of light as both a particle and a wave.

    Example

    In projective geometry, every theorem has a dual statement where the roles of points and lines are interchanged.
  2. 4 the other of a pair (n.)
    C2 Proficiency Technical Math

    one of two things that form a pair, especially in math or logic.

    an object, property, or proof that exists in a relationship of duality with another.

    Example

    The cube is the dual of the octahedron.

    Example

    To solve the optimisation problem, the student first had to derive the dual of the original linear programme.
  3. 5 to expand a road (v.)
    C1 Advanced British English Technical

    to change a road with one lane in each direction into a larger road with two lanes in each direction.

    to convert a single-carriageway road into a dual carriageway.

    Example

    The government plans to dual the main highway to reduce traffic jams.

    Example

    The local council has finally secured the funding required to dual the bypass, a project expected to take eighteen months.

    Usage

    This is a transitive verb, typically used in civil engineering or urban planning contexts.
Origin

PIE word *dwóh₁ Borrowed from Latin dualis (“two”), from duo (“two”) + adjective suffix -alis.

Word family

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