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From Ancient Greek δυάς (duás), δυάδ- (duád-) from δύο (dúo, two), from Proto-Indo-European *duwó, *duwéh₃ (*dwóh₁).[1] The mathematics sense was coined by American scientist (1839–1903) Josiah Willard Gibbs in 1884 in the second half of his book Elements of Vector Analysis.



dyad (plural dyads)

  1. A set of two elements treated as one; a pair.
    Synonyms: couple, duad; see also Thesaurus:duo
    • 1908, W. D. Ross, Metaphysics Book I, translation of original by Aristotle:
      [] positing a dyad and constructing the infinite out of great and small, instead of treating the infinite as one, is peculiar to him; []
    • 2019 January 29, Tom Bissell, “An Anti-Facebook Manifesto”, in New York Times[1]:
      McNamee describes their grip on the company as “the most centralized decision-making structure I have ever encountered in a large company.” Their power dyad is possible only because Facebook’s “core platform,” as McNamee puts it, is relatively simple: It “consists of a product and a monetization scheme.”
  2. (sociology) Two persons in an ongoing relationship; dyadic relationship.
    • 2003, Debra Lieberman, John Tooby, Leda Cosmides, The evolution of human incest avoidance mechanisms [] [2], page 20:
      For each individual in a specific dyad (i.e., mother-offspring, offspring-father, sibling-sibling), []
  3. (sociology) The relationship or interaction itself in reference to a couple.
  4. (music) Any set of two different pitch classes.
  5. (chemistry) An element, atom, or radical having a valence of or combining power of two.
  6. (biology) A chromosome structure, usually X- or V-shaped, consisting of two condensed sister chromatids joined by a centromere.
  7. (biology) A secondary unit of organisation consisting of an aggregate of monads.
  8. (mathematics) A tensor of order two and rank one.

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  1. ^ “dyad”, in The American Heritage Dictionary of the English Language, 4th edition, Boston, Mass.: Houghton Mifflin, 2000, →ISBN.