noun two items of the same kind.
— synonyms: couple, pair, twosome, twain, brace, span, yoke, couplet
Examples
“"For each individual in a specific dyad (i.e., mother-offspring, offspring-father, sibling-sibling),..." Debra Lieberman, John Tooby, and Leda Cosmides - The evolution of human incest avoidance mechanisms: an evolutionary psychological approach, p. 20”