dual

C1 · Advanced grammar Technical

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

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

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

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

C2 · Proficiency Science Academic · Technical

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

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

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

“In projective geometry, every theorem has a dual statement where the roles of points and lines are interchanged.”

C2 · Proficiency Countable noun Mathematics Technical

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

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

“The cube is the dual of the octahedron.”

“To solve the optimisation problem, the student first had to derive the dual of the original linear programme.”

C1 · Advanced British English · Technical

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

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

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

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