dual

US/ˈdul/

adjectiveC1Common in everyday speech and writing · #7,915 of 15,258mostly written

Dual means having two parts or two purposes. Dual carriageway, dual nationality, dual purpose.

It is not the same word as duel, a fight between two people, and the two are constantly confused in writing. A dual carriageway has two separated lanes of traffic in each direction. Dual nationality means holding two passports at once.

Definitions of dual

1adjectivedualHaving two parts or two purposes.C1
“The sofa serves a dual purpose, as a seat by day and a bed at night.”

dual is a quality.

Where it comes from

Latin dualis, of two, comes from duo, two. English once had a dual number in grammar, a separate form for exactly two things, which survives in Old English wit, meaning we two.

Proto-Indo-European
*dwóh₁
Latin
dualis — two
English, today
dual

Built from

duo · Latin — two

Borrowed from Latin dualis (“two”), from duo (“two”) + adjective suffix -alis.

Etymology from Wiktionary, CC BY-SA

Practise this word

dual in the wild

When applied to vector spaces of functions (which are typically infinite-dimensional), dual spaces are used to describe measures, distributions, and Hilbert spaces.
Dual space
Consequently, the dual space is an important concept in functional analysis.
Dual space
Therefore, for many classes of polyhedra defined by their symmetries, the duals belong to a corresponding symmetry class.
Dual polyhedron
The DSi added dual digital cameras, larger screens, more memory, a faster processor, and internal flash memory, and it was later offered in a larger DSi XL model.
Nintendo DS
A dual role (also known as a double role) is an instance of one actor playing two roles in a single production.
Dual role

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From Wikipedia, CC BY-SA 4.0. These sentences were written by other people about their own subjects; they are here to show the word at work, not as anybody’s opinion.

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