A pair of two things, especially in philosophy, mathematics, or sociology; a group of two people or entities considered as a unit.
From Latin 'duad-' and Greek 'duas,' from 'duo' (two). The word entered English in the 17th century as philosophers and mathematicians needed precise terms for paired concepts.
Sociologists love the word 'duad'—it's the technical term for any pair of people (like a friendship or marriage), and they use it to study how two-person relationships work differently from groups of three or more.
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