dual

Alternative forms

• du. (abbreviation, grammar)

Etymology

Borrowed from Latin dualis (“two”), from duo (“two”) + adjective suffix -alis

Pronunciation

• (UK) enPR: dyo͞o'əl, djo͞o'əl; IPA^(key): /ˈdjuː.əl/, /ˈdʒuː.əl/
• (US) enPR: d(y)o͞o'əl; IPA^(key): /ˈd(j)uː.əl/

• Audio (UK)

  (file)

• Rhymes: -ʊəl
• Homophone: duel

Adjective

dual (not comparable)

1. Exhibiting duality; characterized by having two (usually equivalent) components.
2. Acting as a counterpart.
3. Double.

   dual-headed computer

4. (grammar) Pertaining to grammatical number (as in singular and plural), referring to two of something, such as a pair of shoes, in the context of the singular, plural and in some languages, trial grammatical number. Modern Arabic displays a dual number, as did Homeric Greek.
5. (linear algebra) Being the space of all linear functionals of (some other space).
   • 2012, Doug Fisher, Hans-J. Lenz, Learning from Data: Artificial Intelligence and Statistics V, Springer Science & Business Media →ISBN, page 81

     Accordingly, a hyperplane in the sample space is dual to a subspace in the variable space.

6. (category theory) Being the dual of (some other category); containing the same objects but with domain and codomain reversed for all functions.
   • 1992, Colin McLarty, Elementary Categories, Elementary Toposes, Clarendon Press →ISBN, page 77

     Every category is dual to its own dual, so if a statement holds in all categories so does its dual.

Noun

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) dual number The grammatical number of a noun marking two of something (as in singular, dual, plural), sometimes referring to two of anything (a couple of, exactly two of), or a chirality-marked pair (as in left and right, as with gloves or shoes) or in some languages as a discourse marker, "between you and me". A few languages display trial 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.

Verb

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.

   • 1998, Great Britain. Parliament. House of Commons, Parliamentary Debates

     Way back in 1971, the Government of the day first published plans for a high-capacity road network, which included the dualling of the A47 from King's Lynn to Great Yarmouth.

   • 2006, David Lowe, Intermodal Freight Transport, p. 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.

Anagrams

• Auld, Daul, Dula, auld, laud, udal

Pronunciation

• IPA^(key): /d̪ˠuəlˠ/

Etymology 1

From Old Irish dúal (“tress, lock of hair”), from Proto-Celtic *doklos, from Proto-Indo-European *doḱlos (compare Icelandic tagl (“horse’s tail”), Old English tægel, English tail).

Etymology 2

Etymology 3

From Old Irish dúal (“that which belongs or is proper to an individual by nature or descent”), from Proto-Indo-European *dʰewgʰ-.

Mutation

Further reading

• "dual" in Foclóir Gaeilge-Béarla, An Gúm, 1977, by Niall Ó Dónaill.
• “1 dúal” in Dictionary of the Irish Language, Royal Irish Academy, 1913–76.
• “2 dúal” in Dictionary of the Irish Language, Royal Irish Academy, 1913–76.
• Entries containing “dual” in English-Irish Dictionary, An Gúm, 1959, by Tomás de Bhaldraithe.
• Entries containing “dual” in New English-Irish Dictionary by Foras na Gaeilge.

Adjective

dual m, f (plural duais, comparable)

1. dual (having two elements)

Etymology 1

From Old Irish dúal (“that which belongs or is proper to an individual by nature or descent”), from Proto-Indo-European *dʰewgʰ-.

Etymology 2

From Old Irish dúal (“tress, lock of hair”), from Proto-Celtic *doklos, from Proto-Indo-European *doḱlos.

Mutation

Further reading

• “1 dúal” in Dictionary of the Irish Language, Royal Irish Academy, 1913–76.
• “2 dúal” in Dictionary of the Irish Language, Royal Irish Academy, 1913–76.

Adjective

dual (plural duales)

1. dual
2. (grammar) dual