Borrowed from Latin dualis, from duo + adjective suffix -alis.

• (British) enPR: dyo͞oʹəl, jo͞oʹəl; IPA: /ˈdjuː.əl/, /ˈdʒuː.əl/
• (America) enPR: d(y)o͞o'əl; IPA: /ˈd(j)u.əl/

dual (not comparable)

1. Characterized by having two (usually equivalent) components.

   Synonyms: double, twin, Thesaurus:dual

   a dual-motor vehicle

2. Pertaining to two, pertaining to a pair of.

   Synonyms: double, duplicate, Thesaurus:twofold

   dual engine failure

   dual citizenship

3. (grammar) Pertaining to a grammatical number in certain languages that refers to two of something, such as a pair of shoes.

   Coordinate terms: singular, trial, plural

   Modern Arabic displays a dual number, as did Homeric Greek.

4. (mathematics, physics) Exhibiting duality.
5. (linear algebra) Being the space of all linear functionals of (some other space).
6. (category theory) Being the dual of some other category; containing the same objects but with source and target reversed for all morphisms.

   Synonyms: opposite

• French: double, duel, dual
• Italian: duale, doppio
• Portuguese: dual
• Russian: двойно́й
• Spanish: doble, dual

• French: double
• Portuguese: duplo
• Russian: двойно́й
• Spanish: doble

• French: duel
• German: dual
• Portuguese: dual
• Russian: дво́йственный
• Spanish: dual

dual (plural duals)

1. Of an item that is one of a pair, the other item in the pair.
2. (geometry) Of a regular polyhedron with V vertices and F faces, the regular polyhedron having F vertices and V faces.

   The octahedron is the dual of the cube.

3. (grammar) The dual number.
4. (mathematics) Of a vector in an inner product space, the linear functional corresponding to taking the inner product with that vector. The set of all duals is a vector space called the dual space.

• French: duel
• German: Dual, Zweizahl
• Portuguese: dual
• Russian: дво́йственное число́

dual (third-person singular simple present duals, present participle (UK) dualling or (US) dualing, simple past and past participle (UK) dualled or (US) dualed)

1. (transitive) To convert from single to dual; specifically, to convert a single-carriageway road to a dual carriageway.
   • 1994, Great Britain. Parliament. House of Commons, Parliamentary Debates:

     I have to declare an interest and I do so with some ambivalence because if the road is dualled it is likely to take half of my front garden.

   • 2006, David Lowe, Intermodal Freight Transport, page 163:

     The power generation and propulsion systems are dualled to accommodate component failure and maintain propulsion at reduced speed should any part of one system be lost.