(1) A pair. SYN: diad (2). (2) In chemistry, a bivalent element, molecule, or ion. (3) Two people in an interactional situation, e.g., patient and therapist, husband and wife. (4) The double chromosome resulting from division in meiosis. (5) Two units treated as one. (6) A pair of cells resulting from the first meitotic division. (7) The transverse tubule and a terminal cisterna in cardiac muscle cells. [G. dyas, the number two, duality]
