dyad

plural dyads

1. A set of two elements treated as one; a pair.

   […] positing a dyad and constructing the infinite out of great and small, instead of treating the infinite as one, is peculiar to him; […]

   1908, W. D. Ross, Metaphysics Book I, translation of original by Aristotle

   1 more example

   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.”

   2019 January 29, Tom Bissell, “An Anti-Facebook Manifesto”, in New York Times

   Synonyms: couple, duad, brace, couple, couplet, doublet, duad, duet

2. human sciencesTwo persons in an ongoing relationship; a dyadic relationship.

   For each individual in a specific dyad (i.e., mother-offspring, offspring-father, sibling-sibling), […]

   2003, Debra Lieberman, John Tooby, Leda Cosmides, The evolution of human incest avoidance mechanisms […] , page 20

   1 more example

   The southern relationship was a slaveholder-physician dyad, with the slave left outside, unconsulted, uninformed, and with no recourse if she or he was unsatisfied, injured, or killed—a medical nonentity.

   2008, Harriet A. Washington, “Southern Discomfort”, in Medical Apartheid, Knopf Doubleday Publishing Group, page 64

3. human sciencesThe relationship or interaction itself in reference to a couple.
4. entertainmentAny set of two different pitch classes.
5. chemistryAn element, atom, or radical having a valence of or combining power of two.
6. biologyA chromosome structure, usually X- or V-shaped, consisting of two condensed sister chromatids joined by a centromere.
7. biologyA secondary unit of organisation consisting of an aggregate of monads.
8. mathematicsA tensor of order two and rank one.