1. Adjective.  Characterized by having two (usually equivalent) components.
  2. Adjective.  Double.
  3. Adjective.  (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.
  4. Noun.  Of an item that is one of a pair, the other item in the pair.
  5. Noun.  (geometry) Of a regular polyhedron with ''V'' vertices and ''F'' faces, the regular polyhedron having ''F'' vertices and ''V'' faces.
  6. Noun.  (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.
  7. Noun.  (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.

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This entry was last updated on RefTopia from its source on 3/20/2012.