# dual

### adjective

1. consisting of or involving two parts or components usually in pairs

*- dual controls for pilot and copilot*

Similar word(s): multiple, double, duple

2. having more than one decidedly dissimilar aspects or qualities

*- a double (or dual) role for an actor*

Similar word(s): multiple, double, threefold, treble, twofold

3. a grammatical number category referring to two items or units as opposed to one item (singular) or more than two items (plural)

*- ancient Greek had the dual form but it has merged with the plural form in modern Greek*

Similar word(s): plural

#### Sentences with dual as an adjective:

*- dual-headed computer*

### noun

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.