(Chem.) An element, atom, or radical having a valence or combining power of two.
adjective
Dyad adj. (Chem.) Having a valence or combining power of two; capable of being substituted for, combined with, or replaced by, two atoms of hydrogen; as, oxygen and calcium are dyad elements. See Valence.
... light and gravitation, each being bipolar; gravitationnorth and south, or attraction and repulsion; lighteast and west, or contraction and dilation; and gold being the tetrad, or interpenetration of both, as water was the dyad of light, and iron ... — Literary Remains (1) • Coleridge
... of one is a monad; of two, a dyad; three, a triad; four, tetrad; five, pentad; six, hexad, etc. It is also said to be monovalent, di- or bivalent, etc. This theory of bonds shows why an atom cannot exist alone. It would have free or unused bonds, and hence must combine ... — An Introduction to Chemical Science • R.P. Williams
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