<p><strong>Noun</strong></p><ul><li>a group of two; couple; pair.</li><li>a secondary morphological unit, consisting of two monads: a chromosome dyad.</li><li>the double chromosomes resulting from the separation of the four chromatids of a tetrad.</li><li>an element, atom, or group having a valence of two.</li><li>two vectors with no symbol connecting them, usually considered as an operator.</li><li>two persons involved in an ongoing relationship or interaction; the relationship or interaction itself.</li></ul><p><strong>Adjective</strong></p><ul><li>of two parts; dyadic.</li></ul>