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(dī′ăd′, -əd)
n.
1. Two individuals or units regarded as a pair: the mother-daughter dyad.
2. Biology One pair of homologous chromosomes resulting from the division of a tetrad during meiosis.
3. Mathematics
a. A function that draws a correspondence from any vector u to the vector (v·u)w and is denoted vw, where v and w are a fixed pair of vectors and v·u is the scalar product of v and u. For example, if v = (2,3,1), w = (0,-1,4), and u = (a,b,c), then the dyad vw draws a correspondence from u to (2a + 3b + c)w.
b. A tensor formed from a vector in a vector space and a linear functional on that vector space.

[From Greek duas, duad-, from duo, two; see dwo- in Indo-European roots.]

(ˈdaɪæd)
n
1. (Mathematics) maths an operator that is the unspecified product of two vectors. It can operate on a vector to produce either a scalar or vector product
2. (Chemistry) an atom or group that has a valency of two
3. a group of two; couple
[C17: from Late Latin dyas, from Greek duas two, a pair]

(ˈdaɪ æd)

n.
1. a group of two; couple; pair.
2. the double chromosomes resulting from the separation of the four chromatids of a tetrad.
3. an element, atom, or group having a valence of two.
4. Math. two vectors with no symbol connecting them, usu. considered as an operator.
5.
a. two people involved in an ongoing relationship or interaction.
b. the relationship or interaction itself.
[1665–75; < Greek dyad-, s. of dyás pair <dý(o) two]
ThesaurusAntonymsRelated WordsSynonymsLegend:
 Noun 1 dyad - two items of the same kind    fellow, mate - one of a pair; "he lost the mate to his shoe"; "one eye was blue but its fellow was brown"2, II, two, deuce - the cardinal number that is the sum of one and one or a numeral representing this numberdoubleton - (bridge) a pair of playing cards that are the only cards in their suit in the hand dealt to a player
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