a group of two; couple; pair.

Biology .

a secondary morphological unit, consisting of two monads

a chromosome dyad.

the double chromosomes resulting from the separation of the four chromatids of a tetrad.

Chemistry . an element, atom, or group having a valence of two. Compare monad , triad ( def. 2a ) .

Mathematics . two vectors with no symbol connecting them, usually considered as an operator.

Sociology .

two persons involved in an ongoing relationship or interaction.

the relationship or interaction itself.

of two parts; dyadic.