n. [ L. dyas, dyadis, the number two. Gr. &unr_;: cf. F. dyade. See two, and cf. Duad. ] 1. Two units treated as one; a couple; a pair. [ 1913 Webster ]

2. (Chem.) An element, atom, or radical having a valence or combining power of two. [ 1913 Webster ]

a. (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. [ 1913 Webster ]

a. [ Gr. &unr_;, fr. &unr_; two. ] Pertaining to the number two; of two parts or elements. [ 1913 Webster ]

Dyadic arithmetic, the same as binary arithmetic. [ 1913 Webster ]