dual

adjective

• 1 [attributive] consisting of two parts, elements, or aspects:their dual role at work and home dual-language texts in English and Italian
• Grammar (in some languages) denoting an inflection that refers to exactly two people or things (as distinct from singular and plural).
• (in an aircraft) using dual controls: a dual flight

• 2 (often dual to) Mathematics (of a theorem, expression, etc.) related to another by the interchange of particular pairs of terms, such as ‘point’ and ‘line’.

noun

• 1 Grammar a dual form of a word.
• [mass noun] the dual number.

• 2 Mathematics a theorem, expression, etc., that is dual to another.

verb (duals, dualling, dualled)

• convert (a road) into a dual carriageway: though there are no plans to dual the road, a public consultation on the A64 is set to start before the end of the year