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dual

[doo-uh l, dyoo-] /ˈdu əl, ˈdyu-/
adjective
1.
of, pertaining to, or noting two.
2.
composed or consisting of two people, items, parts, etc., together; twofold; double:
dual ownership; dual controls on a plane.
3.
having a twofold, or double, character or nature.
4.
Grammar. being or pertaining to a member of the category of number, as in Old English, Old Russian, or Arabic, that denotes two of the things in question.
noun, Grammar
5.
the dual number.
6.
a form in the dual, as Old English git “you two,” as contrasted with ge “you” referring to three or more.
Origin
1535-1545
1535-45; < Latin duālis containing two, relating to a pair, equivalent to du(o) two + -ālis -al1
Related forms
dually, adverb
Can be confused
dual, duel.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Examples from the web for dual
  • dual agency, by which an agent represents both buyer and seller, is becoming more common.
  • Critics say that dual citizenship implies diminished loyalty to the motherland.
  • Such dual behavior was then unknown to medical science.
  • We have many intersections with dual left-turn lanes.
  • But he may be the first to show the duelling demi-urges behind his dual reality exchanging trade secrets over dessert.
  • Composting serves dual purposes for the green gardener.
  • The human history is rich on examples where the excessive stress on one side of any dual perspectives issues leads us to problems.
  • He hopes to use these dual interests to double his impact on conservation efforts throughout the world.
  • If you don't have a dual flush toilet put a brick into the cistern to reduce capacity.
  • Then maybe if decided to, squeeze in a dual between the dinosaurs.
British Dictionary definitions for dual

dual

/ˈdjuːəl/
adjective
1.
relating to or denoting two
2.
twofold; double
3.
(in the grammar of Old English, Ancient Greek, and certain other languages) denoting a form of a word indicating that exactly two referents are being referred to
4.
(maths, logic) (of structures or expressions) having the property that the interchange of certain pairs of terms, and usually the distribution of negation, yields equivalent structures or expressions
noun
5.
(grammar)
  1. the dual number
  2. a dual form of a word
verb duals, dualling, dualled
6.
(transitive) (Brit) to make (a road) into a dual carriageway
Derived Forms
dually, adverb
Word Origin
C17: from Latin duālis concerning two, from duo two
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for dual
adj.

c.1600, from Latin dualis, from duo "two" (see two). Related: Dually.

Online Etymology Dictionary, © 2010 Douglas Harper
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dual in Technology
mathematics
Every field of mathematics has a different meaning of dual. Loosely, where there is some binary symmetry of a theory, the image of what you look at normally under this symmetry is referred to as the dual of your normal things.
In linear algebra for example, for any vector space V, over a field, F, the vector space of linear maps from V to F is known as the dual of V. It can be shown that if V is finite-dimensional, V and its dual are isomorphic (though no isomorphism between them is any more natural than any other).
There is a natural embedding of any vector space in the dual of its dual:
V -> V'': v -> (V': w -> wv : F)
(x' is normally written as x with a horizontal bar above it). I.e. v'' is the linear map, from V' to F, which maps any w to the scalar obtained by applying w to v. In short, this double-dual mapping simply exchanges the roles of function and argument.
It is conventional, when talking about vectors in V, to refer to the members of V' as covectors.
(1997-03-16)
The Free On-line Dictionary of Computing, © Denis Howe 2010 http://foldoc.org
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