Exhibiting duality; characterized by having two (usually equivalent) components.
Acting as a counterpart.
Double.
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.
Being the space of all linear functionals of (some other space).
Being the dual of (some other category); containing the same objects but with source and target reversed for all morphisms.
Of an item that is one of a pair, the other item in the pair.
Of a regular polyhedron with V vertices and F faces, the regular polyhedron having F vertices and V faces.
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.
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.
To convert from single to dual; specifically, to convert a single-carriageway road to a dual carriageway.
Arranged, regular combat between two private persons, often over a matter of honor.
Historically, the wager of battle (judicial combat)
Any struggle between two contending persons, groups or ideas.
To engage in a battle.
