Dual

/ˈdjuː.əl/

noun

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.
“The octahedron is the dual of the cube.”
(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.

To convert from single to dual; specifically, to convert a single-carriageway road to a dual carriageway.

Exhibiting duality; characterized by having two (usually equivalent) components.
Acting as a counterpart.
Double.
“a dual-headed computer”