# Definify.com

## Du′al

,
[L.
dualis
, fr.
duo
two. See
Two
.]
Expressing, or consisting of, the number two; belonging to two;
as, the
dual
number of nouns, etc.
, in Greek.
Here you have one half of our
dual
truth.
Tyndall.

## DUAL

,
[L., two.] Expressing the number two; as the dual number in Greek.

# Dual

## German

### Noun

Dual m (genitive Duals, plural Duale)

1. (grammar) dual, dual number

# dual

## English

### Alternative forms

• (abbreviation, grammar): du.

dual (not comparable)

1. Exhibiting duality; characterized by having two (usually equivalent) components.
2. Acting as a counterpart.
3. Double.
4. (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.
5. (linear algebra) Being the space of all linear functionals of (some other space).
• 2012, Doug Fisher, Hans-J. Lenz, Learning from Data: Artificial Intelligence and Statistics V, Springer Science & Business Media (ISBN 9781461224044), page 81
Accordingly, a hyperplane in the sample space is dual to a subspace in the variable space.
6. (category theory) Being the dual of (some other category); containing the same objects but with domain and codomain reversed for all functions.
• 1992, Colin McLarty, Elementary Categories, Elementary Toposes, Clarendon Press (ISBN 9780191589492), page 77
Every category is dual to its own dual, so if a statement holds in all categories so does its dual.

### Noun

dual (plural duals)

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.

## Irish

### Pronunciation

• IPA(key): /d̪ˠuəlˠ/

### Etymology 1

From Old Irish dúal (tress, lock of hair), from Proto-Celtic *doklo-, from Proto-Indo-European *doḱ-lo- (compare Icelandic tagl (horse’s tail), Old English tægel, English tail).

#### Noun

dual m (genitive singular duail, nominative plural duail)

#### Verb

dual (present analytic dualann, future analytic dualfaidh, verbal noun dualadh, past participle dualta)

1. to twine
2. to braid, coil
3. to interlace, fold

### Etymology 2

#### Noun

dual m (genitive singular duail, nominative plural duail)

1. dowel
2. knot (in timber)

### Etymology 3

From Proto-Indo-European *dʰewgʰ-.

dual

1. native, natural
Is dual dó a bheith leisciúil. ― He is naturally lazy.
2. proper, fitting
3. in the natural order of things
4. fated
5. possible

### Mutation

Irish mutation
dual dhual ndual
Note: Some of these forms may be hypothetical. Not every
possible mutated form of every word actually occurs.

## Portuguese

dual m, f (plural duais, comparable)

1. dual (having two elements)

## Scottish Gaelic

### Noun

dual m (genitive singular duail, plural dualan)

1. birthright

### Noun

dual m (genitive singular duail, plural dualan)

1. curl, lock of hair
2. plait, strand, braid, or fold
3. ringlet