(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.”
Double.
“a dual-headed computer”
noun
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.”
Of an item that is one of a pair, the other item in the pair.